Both todd and zack earn the same salary. todd spent $716 and zack spent $128. then zack had 4 times the amount of money todd had left. how much is their salary? tell me how and what your answer is?

They both earn the same salary.  Call it ' S '.

After Todd spent 716, he had (S - 716) left.

After Zack spent 128, he had (S - 128) left.

The question says that Zack has 4 times as much as Todd has, so

(S - 128) = 4 times (S - 716)

Eliminate parentheses on the right side:

S - 128 = 4S - 2,864

Subtract ' S ' from each side:

-128 = 3S - 2,864

Add 2,864 to each side:

2,736 = 3S

Divide each side by 3 :

912 = S


Check:
After Todd spends 716, he has (912 - 716) = 196 left.
After Zack spends 128, he has (912 - 128) = 784 left.
784/196 = exactly 4 times. 
yay !