Question

x+12y=68 x=8y-12

Answer 1

This is simple substitution.
Plug x=8y-12 into the first equation.

8y-12+12y=68
20y-12=68
20y=80
y=4

Then plug that value of y back into the original equation to get the value of x.

x=8(4)-12
x=32-2
x=20