Answer:
A camera is selling for $7.50 off the regular price. It was marked down 15%.
Let the regular price be x
We can solve as follows:

=> 
=> x = 8.82
The correct regular price is $8.82.
A student used the equation:
15(7.5) = Original price
and found the regular price of the camera to be $112.50.
The student did the wrong calculation. He simply took 15% of selling price.
He should have done 15% of regular price that will come to be the selling price.