Answer
$k\gt critical~value$: null hypothesis is not rejected.
There is not enough evidence to conclude that $M\lt8$
Work Step by Step
$H_0:~M=8$ versus $H_1:~M\lt8$
$n=13+8=21$
$Critical~value=6$
Left-tailed test:
$k=number~of~plus~signs=8$
Since $k\gt critical~value$, we do not reject the null hypothesis.
