2x - 10 y = -30

Question

x - 5y = 20

Answer 1

just to use smaller numbers, divide eq#1 by 2 to get
x-5y = -15
Now, substitute from eq#2 x = 5y+20 and you have
5y+20-5y = -15
20 = -15
No joy here. It's either a trick question or there's a typo.