y = x + 5 (eq. 1)
y = 2x - 7​ (eq. 2)
Substituting equation 1 into equation 2, we get:
x + 5 = 2x - 7
5 = 2x - 7 - x
5 = x - 7
5 + 7 = x
12 = x
Replacing this result into the first equation:
y = 12 + 5
y = 17
