Answer
The minimum weight of block C is $~~66~N$
Work Step by Step
To prevent A from sliding, the force of static friction on block A must be equal to the weight of block B. We can find the minimum weight of block C:
$(m_A~g+m_c~g)~\mu_s = m_b~g$
$m_c~g~\mu_s = m_b~g - m_A~g~\mu_s$
$m_c~g = \frac{m_b~g - m_A~g~\mu_s}{\mu_s}$
$m_c~g = \frac{(22~N) - (44~N)~(0.20)}{0.20}$
$m_c~g = 66~N$
The minimum weight of block C is $~~66~N$
