Can some one help me I need to learn how to solve this I know I need to use y = mx + b

A doctor measured a baby’s length at 21 inches when the baby was one month old. At the baby’s six-month doctor’s appointment, the baby’s length was 26 inches. Find the baby’s length when the baby is one year old if his length increases at a constant rate.

Question

Can some one help me I need to learn how to solve this I know I need to use y = mx + b

 A doctor measured a baby’s length at 21 inches when the baby was one month old. At the baby’s six-month doctor’s appointment, the baby’s length was 26 inches. Find the baby’s length when the baby is one year old if his length increases at a constant rate.

anonymous · Answer

31 inches i think? this suppose to be a A.P term

campbell_st · Answer

ok... 

if you want to use the straight line y = mx + b

then you need to find the slope  using the given data points (1, 21) and (6, 26). 

are you able yo calculate the slope for the 2 points above..?

campbell_st · Answer

@Zheng... why not let the asker... answer the questions...

anonymous · Answer

So do point slope formula with what cambell provided...do you know how to do that?

anonymous · Answer

31 is the answer.
am I rgt?

anonymous · Answer

No your answer is not a number

anonymous · Answer

Its going to be in terms of x

campbell_st · Answer

@rambo... I have no idea

campbell_st · Answer

actually its incorrect @rambo

anonymous · Answer

Do (26-21)/(6-1) to do point slope formula, I basically just gave you the answer

anonymous · Answer

@ilikephysics2 you are wrong.
yo can get number.

anonymous · Answer

No you can't its in y = mx+b

campbell_st · Answer

lol..@ilikephysics2 your are busting to answer this...

anonymous · Answer

i guess you can make it a number, or leave it in terms of x

anonymous · Answer

Cambell you have no idea what you are doing do you?

campbell_st · Answer

you are asked to use the linear relationship y = mx + b to answer the question @ilikephysics2 , not just get the get the equation

anonymous · Answer

so use it in that formula, thats all she needs

campbell_st · Answer

actually I do know how to solve this question

anonymous · Answer

okay guys -.- thanks lol

anonymous · Answer

btw i was trying to help her do the formula not just giving her the answer

campbell_st · Answer

why not wait as see if she knows what to do...rather that saying... this is it... but its all just maths

anonymous · Answer

let me explain you.
 
 y=mx+b
 y=lenght
 m=month
 x,b = constant
 
 at the time of birth,
 y=21
 m=1
 21=x+b
 
 at 6th mont,
 y=26
 m=6
 26=6x+b
 
 we have
 x+b=21
 6x+b=26
 
 by solvinf this 2,
 we get,
 x=1
 b=20
 now at one year,
 y=?
 m=12
 x=1
 b=20
 
 y=12*1 + 20
 y=32

anonymous · Answer

hope every1 got the answer.