A nail pinned onto a rotating waterwheel moves according to this function: h(t) = -5sin[pi/4(t-1)] +2.5 where t is the time in seconds and h is height in metres

*Calculate the durations of time where the nail is underwater for the first 24 seconds

im kinda confused as to what to sub in for h, because i know the highest the wheel goes is 7.5m, and the lowest it goes is -2.5m. Should my h be zero or 2.5?

thanks in advance