Answer:
$300
Step-by-step explanation:
- 150/12 to figure out how much to install one yard ($12.50)
- 24•12.50=300
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

19. 5x - 5 = 3x -9
2x = -4
x = -2
19. Answer is A