Question 831654
EDIT: THIS solution contained a mistake, now been fixed!
8X=200+10(X-40), dropping the dollar symbol, focusing just on the numbers without money unit;
8X=200+10X-400, Distributive Property
0=200-400+2X, Additive Inverse of 8X and Commutative Property for Addition
2X-200=0, (.......what's my reason?)
2X=200, 
X=100, {{{X=100}}}