The credit remaining on a phone card (in dollars) is a linear function of the total calling time made with the card (in minutes). The remaining credit after 35 minutes of calls is $24.40, and the remaining credit after 71 minutes of calls is $18.64 . What is the remaining credit after 104 minutes of calls?

Question

zpupster · Answer

are you there??

anonymous · Answer

yeah im here! :D

zpupster · Answer

this is a little involved 
since it is a line  we need the slope
look at the question and come up with 2 ordered pairs (x,y)

anonymous · Answer

how about (7,5)

anonymous · Answer

oh were you asking me to make one ?

anonymous · Answer

)Point A is located at negative 7 over 10 and point B is located at negative 2 over 10. What is the distance between points A and B?

anonymous · Answer

what sisi?

zpupster · Answer

no from the question

zpupster · Answer

hhow about
(35,24.40) and (71,18.64) our third would be (104, y)

zpupster · Answer

$$m=\frac{ y2-y1 }{ x2-x1}$$

anonymous · Answer

oh okidoke !

zpupster · Answer

we will use the above formula to find a slope
can oyu plug the values in??

anonymous · Answer

would i basically just use the last two points?

zpupster · Answer

x2=35
x1=71
and
y2=24.40
y1 = 18.64

do oyu see now??

anonymous · Answer

yeuup! 
m= y1-y2/x1-x2
m=18.64-24.40/71-35

anonymous · Answer

m=-5.76/36
now what?

zpupster · Answer

ok do the math

anonymous · Answer

-.16

anonymous · Answer

thats what i got at least

zpupster · Answer

m=-5.76/36=-.16
ok?

anonymous · Answer

yeup!

zpupster · Answer

now we need to use the point slope form
$$y-y1 = m(x-x1)$$

zpupster · Answer

use (35,24.40)

$$y-24.4=-.16(x-35)$$

zpupster · Answer

you nedd to put it in this slope intercept form form
$$y=mx+b$$

anonymous · Answer

sorry i'm doing two things at once here okidoke 
im not quite sure where to go from here im at 
y-24.4=-.16x+5.6

anonymous · Answer

because i did the math on the one side

zpupster · Answer

add 24.4 to both sides

anonymous · Answer

oh right ah ! okidoke 
y=-.16x=30

zpupster · Answer

now we have our line
and we know x = 104 for our third point so plug it in the 
y=-.16(104) +30
what do you get??

anonymous · Answer

46.64!

anonymous · Answer

but that doesn't make any sensee

zpupster · Answer

try one more time

anonymous · Answer

oh dangit okidoke
uhh 13.36!!

zpupster · Answer

yep and that is your answer
good job!!
you can see the point falls on our line-graph

anonymous · Answer

awesome thanks so much dude ! :DD

zpupster · Answer

no problem!!
i would advise you glance over this again and pay attention to the steps.

anonymous · Answer

For sure thanks again! :)