your solving for variable x
do move all the terms containing x to the left and all other terms to the right
so we going to add -0.5y to each side of the equation
0.2x + 0.5y + -0.5y = 4 + -0.5y
them combine like terms 0.5y + -0.5y =0.0
0.2x +0.0 =4 + -0.5y
0.2x = 4 +-0.5y
Divide each side by 0.2
x= 20 +-2.5y
x=20+ -2.5y
