You probably have done something like this and are confused by the directions.
Step One
Write down the equation and the givens.
P = 425
x is what you are trying to isolate.
P = 25x - (10x + 250)
Step Two
Remove the brackets on the right.
P = 25x - 10x - 250 Notice all those minus signs. The one on the outside of the brackets gets distributed just as thought there was a (say) - 5
Step Three
Collect the like terms on the right.
P = 15x - 250
Step Four
This really doesn't require a separate step, but I should have done it at the beginning. Put in P = 425
425 = 15x - 250
Step 5
Add 250 to both sides.
425 + 250 = 15x
675 = 15x
Step Six
divide by 15
675 / 15 = x
45 = x
He has to sell 45 calculators.
