Question

y=-5
5x+4y=-20
it say solve by substitution

Answer 1

5x + (4 · -5) = -20 
5x - 20 = -20 
5x = 0
x = 0

Answer 2

$y=-5\\5x+4y=-20 \\\\5x+4 \cdot (-5)=-20 \\\\5x-20=-20\ \ | \ add\ 20\ to\ both\ sides \\\\5x=0 \ \ | \ divide \ both \ sides\ by\ 5\\\\x=0$