here nothing is told about n, so in that case we'll take n = infinity.
when n = infinity,
$S$ = $\frac{T_{n}}{t_{p}}$
where $T_{n}$ is the time to execute a single instruction in Non-pipelined processor.
$t_{p}$ is the clock cycle time in pipelined processor.
So, $T_{n}$ = CPI * 10ns = 14ns
$t_{p}$ = 2 ns
S = 7