You have the following system of equations:
y = 1/2 x + 4
x - y = 8
to solve by substitution, proced as follow:
replace the expression y = 1/2 x + 4 into the second equation, and then solve for x:
x - (1/2 x + 4) = 8 eliminate parenthesis
x - 1/2 x - 4 = 8 simplify like terms left side
1/2 x - 4 = 8 add 4 both sides
1/2 x = 8 + 4
1/2 x = 12 multiply by 2 both sides
x = 12(2)
x = 24
next, replace the value x = 24 into the expression y = 1/2x + 4 to obtain y:
y = 1/2 (24) + 4
y = 12 + 4
y = 16
Hence, the solution to the given system of equations are:
x = 24
y = 16