Ps. Make sure yoi dont times the (X x 8) by -4 the -4 is by itself.
I personally found it easier thinking if there is a difference of 4 between 6 x X and 8x X then it must be 2x2 as the difference between 6 and 8 is 2. therefore 4 divided by 2 = 2 and 2 x 2 = 4