252, because 2x2x3x3x7 = 252
If it’s 15 per hour then the answer is 15
So, h(t) is how far is Daniel's head from the surface of the water, namely the surface itself is when the height is nill, so his head is at the surface and the height of it is just 0, thus h(t) = 0. Namely, what is "t" when h(t) is 0?

clearly the seconds cannot be a negative unit, so is not -3/2.
The solution is 2. -3+5=2