Two questions that are giving me trouble; could someone please show me how?

Question One

A mushroom was observed while growing, and all linear dimensions were growing proportionately. Therefore, the volume increased according to the formula WhereLis any linear dimension andcis a constant. Show that

Using differentials find the percentage error ingislis measured accurately butThas an error of 1%

Question TwoThe acceleration due to gravity

gcan be determined by measuring the period of swing of a pendulum. If the length of the pendulum island the measured period isT, thengis given by the formula