Answer
$k\gt critical~value$: null hypothesis is not rejected.
There is not enough evidence to conclude that the median number of hours that students talk on the phone per week is more than 15.
Work Step by Step
$H_0:~M=15$ versus $H_1:~M\gt15$
$number~of~plus~signs=13$
$number~of~minus~signs=7$
$n=20$ (small sample)
$Critical~value=5$
(According to table XI, for $n=20$ and $α=0.05$ (one tail))
Right-tailed test:
$k=number~of~minus~signs=7$
Since $k\gt critical~value$, we do not reject the null hypothesis.
