Simplify each express so there is only one positive power for each base.

Hello mate!

if we define 15 hours as the 100%, we need to know wich percent represents 18 hours.

We can do it by dividing it by the initial time, and multiplying it by 100%:

18/15*100% = 1.2*100% = 120%

So the first week she spent 15 hours (the 100%) and the second week she spent 18 hours (120%)

the difference between these times is 18 - 15 = 3 hours, or in percentages: 120% - 100% = 20%

this means that she spent 20% more time in the second week than the first week. Then, she was wrong.