Question

Which could be the first step in solving this system of equations by substitution?

y = 7x

y - x = 15

Answer 1

The first step is to replace the y in y-x=15 with 7x (we can do this because the first equation tells us that they're equal)

solve and get

(2.5,17.5)

or x= 2.5 y=17.5

Explanation:

The first step is to recognize that y=7x which means that we can just replace the y in the second equation with 7x

7x-x=15

6x=15

x=2.5

Then we can solve for y

y=7(2.5)

y=17.5