About how long does it take ocean water to travel around a gyre?

The diagram shows a series of volcanic island and a hot spot determine the direction of movement of the tectonic plate that for the island

(a) assume the equation x = at^3 + bt describes the motion of a particular object, with x having the dimension of length and t having the dimension of time. determine the dimensions of the constants a and b. (use the following as necessary: l and t, where l is the unit of length and t is the unit of time.) (b) determine the dimensions of the derivative dx/dt = 3at^2 + b. (use the following as necessary: l and t, where l is the unit of length and t is the unit of time.)

What is the angular momentum of the bar about the axle?