What you have type in

-8(6+6x)+4(-3+6x)

is not an equation, but expression, so the solver simplifies it up to 

-24x - 60

thus, there is no solution for "x".

However, is you type in the equation

-8(6+6x)+4(-3+6x) = 0

you will get the following solution for "x":

x = -5/2

x = -2 1/2