A physics student spends part of her day walking between classes or for recreation, during which time she expends energy at an average rate of 270 . The remainder of the day she is sitting in class, studying, or resting; during these activities, she expends energy at an average rate of 100 .

If she expends a total of 1.5×107 of energy in a 24-hour day, how much of the day did she spend walking?

Hello, I don't know how to solve this problem .. but I took the answer from a site
and the answer is 10.39 hours but the system said that it's wrong and try again
and when i submitted it , they give me a note which said :