Stefan sells Jin a bicycle for $138 and a helmet for $16. The total cost for Jin is 40% of what Stefan spent originally to buy the bike and helmet. How much did Stefan spend originally?

Stefan originally spent $61.60.

Explanation:
Equation: 40/100=x/154
100 is the whole because it is 40% out of a hundred. 154 is the sum of how much Jin bought the bike and helmet for. You would then be able to simplify 40/100 to 4/10. 154 divided by 10 would be 15.4. You would do the same to the numerator, so multiply 4x15.4. That would give you the 40% of what the bike and helmet were originally bought for.