Think about what the normal trig function would look like. In part a, looks something like:
h(t)=Acos (mt- h) + k where A is amplitude, m adjusts the speed of rotation, h shifts left and right, and k is the height.
Remember that cos (t)=1 at the highest point, and cos (t) = -1 at the lowest point. Then just play around with the number till you get it to work out correct.