Which method of solving system of equations should I use for this equation, and what is the answer? (No matter what method I use, I can't figure this out) I would appreciate it if someone can help me out here.

y = 5x + 10
y = 7.5x + 20

y = 5x + 10

y = 7.5x + 20
just use substitution

7.5x + 20 = 5x + 10
2.5x = -10
x = -10/2.5 = - 4