I need help with $part$ $c$ of the following problem:
An accountant has a salary scheme as outlined below.
STARTING SALARY £16,000. ANNUAL INCREASES OF £1,000 GUARANTEED THEREAFTER.
Let £$u_n$ denote the accountant's salary at the beginning of the the $n$ th year, after any increases which are then due have been added.
a) Write down the values of $u_1$, $u_2$, $u_3$ and $u_4$.
Ans: $u_1=16000$, $u_2=17000$, $u_3=18000$, $u_4=19000$
b) Find a formula for $u_n$
Ans: $u_n=1000n+15000$
c)Find the value of $n$ for which $u_{n+1}=1.04u_n$ (that is corresponding to an annual increase of 4%).
Ans: ?