Question

use substitution method to find x and y for 7x + 5y = -31 and -4x + y = 37

Answer 1

(1) 7x + 5y = -31
(2) -4x + y = 37

first we choose an equation (either of the two) and represent one of the variables in terms of the other,, in this case we choose (2), and represent y in terms of x:
-4x + y = 37
y = 37 + 4x

we then substitute this equation to (1):
7x + 5y = -31
7x + 5(37 + 4x) = -31
7x + 185 + 20x = -31
27x = -216
x = -8

substitute this value of x to either equation:
-4(-8) + y = 37
y = 5

so there,, :)