I thing the answer is 7 days
Think About It: If You work 1 times as long, you are working the same amount of time. If you are working more than 1 times as much, you would be working more hours.
3.5 x 1 = 3.5
3.5 x 1.5 = 5.25
So your answer is more
F(x,y) =3x + 5y (hope this helps )
