Okay, to do this, we need to do the Cross-Product Method. On one side, it will be x/90, and the other side will be 15/100. So, after we multiply 90 by 15, and also multiply 100 by x, out new equation is going to be 100x = 1350. After dividing 1350 by 100, we get 13.5
Answer: 15% of 90 hours is 13.5 hours.