5*(c - 4) - x*(4 - c)
-20 + 5*c - x*(4 - c)
-20.0 + 5.0*c - x*(4.0 - c)
-20 + 5*c + x*(-4 + c)
(-4 + c)*(5 + x)
-20 - 4*x + 5*c + c*x