Answer
$k\leq critical~value$: null hypothesis is rejected.
There is enough evidence to conclude that $M\gt12$.
Work Step by Step
$H_0:~M=12$ versus $H_1:~M\gt12$
$number~of~plus~signs=11$
$number~of~minus~signs=3$
$n=11+3=14$ (small sample)
$Critical~value=3$
(According to table XI, for $n=14$ and $α=0.05$ (one tail))
Right-tailed test:
$k=number~of~minus~signs=3$
Since $k\leq critical~value$, we reject the null hypothesis.
