Question

Solve the system of equations by substitution. 9x+7y=31, x=54-8y

Answer 1

replace the x in 9x with (54-8y)

So the equation would now read 9(54-8y)+7y=31

Answer 2

Then isolate the y to one side and you will have your answer as expressed in terms of y

Answer 3

9(54-8y)+7y=31
486-72y+7y=31
486-65y=31
solve for y

Answer 4

do you divide 65 by both sides?

Answer 5

not yet.
subtract 486 in both sides first
486-486-65y=31-486

Answer 6

which would be 455-65y=31 right? then you subtract 65?

Answer 7

if you subtract a positive 486 from a negative 486 is 0,
31-486= -455
-65y=-455
then you have to solve for y by dividing 65 in both sides

Answer 8

so then y=7?

Answer 9

you got it!
good job!

Answer 10

then if you want to solve for y you plug 7 where the y is in the original equation and do the same

Answer 11

would it be 7=54-8y?

Answer 12

no, you put it where the y is.
x=54-8(7)

Answer 13

because you are solving for x

Answer 14

would the whole answer be (-2,7)?

Answer 15

yep!

Answer 16

Thank you for your help :)

Answer 17

no problem!