Question 267714
what is the substitution for
1.) 4y+4x=40
2.) y=3x-30

Based on 2.) we can substitute 3x-30 for y in equation 1.) giving:

4*(3x-30)+4x = 40
12x-120+4x = 40
16x = 160
x = 10

Now we can substitute 10 for x in equation 2.) to determine y.