Convert term-to-term to position-to-term

(4 marks) A geometric sequence has $u_1 = 5$ and term-to-term rule $u_{n+1} = 3u_n$.

(a) Write down the first four terms. (1) (b) Write the position-to-term (nth term) rule. (2) (c) Hence find $u_8$. (1)