What criteria might be used to establish someone as an expert witness

Which is the best for showing percentages of different types of cars sold(gas hybrid , electric , other ) in the united states ?

(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.)

To a of 4 x hz is 1. 0. mm nm nm