Can someone help me with this question? (see below)

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.)

Frank just graduated from eighth grade. assuming exactly four years from now he will graduate from high school how many seconds does he have until his high school graduation