Answer
$10~N\cdot m$
Work Step by Step
We know that
$f_A=\mu_s N_A$
We plug in the known values to obtain:
$f_A=0.1\times 100N=10N$
As moment at point O is $0$
$\implies \Sigma M_{\circ}=0$
$\implies M=f_A(1)$
$\implies M=10(1)=10~N\cdot m$