Use addition or substitution to find the value of y for this set of equations.

Question

4x + 13y = 40
4x + 3y = -40

Answer 1

I would subtract them to get
10y = 80
y = 8
back into the second:
4x + 24 = -40
4x = -64
x = -16

Answer 2

Use addition or substitution to find the value of x for this set of equations.

2x - 3y = -15
x = 4y