The answer would be C. (He counted Yolanda's candy as his own).
This is found by multiplying 500 (starting number of candy) and .64 (percentage divided by a hundred). Thjs would guve you 320, which you would then subtract from the starting number of candy (500) to get 180. 180 is Yolanda's number of candy, which gives you the answer.
Answer:
The step 4 is not what he should have done. But the wrong is step 5, because if he added -2x both sides, it would give the following equation:

and not 
Note that in step 4 he should have added 2x and not -2x to both sides, but we still have the equality. The problem is that step 5 is totally wrong.
I don't know what answer is expected to this question, but I would mark step 5, because this is mathematically wrong.
Solving the equation

Using distribution

Add
both sides


Add 12 both sides

Divide both sides by 5

13. Four observations:
1. m<SWT = 90° (given)
2. QW = TW (given)
3. m<RWS = m<UWV (vertical angle pair)
4. m<RWU = 180° (straight angle)