David needs to raise $250, and he currently has $160 and earns $7.50 an hour.
Let x=number of hours he works, then:
Solve for x and find the number of hours he has to work to have $250:
1. Subtract 160 from both sides of the equation:
2. Divide both sides by 7.50:
Thus, David must work 12 hours to have $250 to buy the video game system.