How many solutions does this linear system have
y = 2x - 5
-8x - 4y = -20

replace the 1st equation into the 2nd one for y
-8x-4(2x-5) = -20
-8x-8x+20 =-20
-16x+20 = -40
-16x=-40
x = 5/2 = 2.5
y = 2x-5 - 2(2.5) - 5 = 5-5 = 0
one solution (2.5,0)