Equation 1 of Problem 4

Expand the equation: \begin{align} ∑M_A=Mgx_1-mgx_2 &\cssId{Step1}{=0}\\[3px] &\cssId{Step2}{=m·g·x_1-m·g·x_2}\\[3px] &\cssId{Step3}{M_A·m-m·g(x_1-x_2)=0}\\[3px] &\cssId{Step4}{-m·g(x_1+x_2)=M_A}\\[3px] &\cssId{Step5}{M_A=m·g·d}\\[3px] &\cssId{Step6}{m= \frac{M_A}{g·d}}\\[3px] \end{align}

1. In the first step we make the equation of the Moment with the point of reference A
2. In the second step we make the equation of normal force and the gravity force
3. In the third step we isolate the M_A with the mass, the gravity and the distance
4. In the fourth step we isolate the M_A again with the mass, the gravity and the distance
5. In the fiveth step we make the equation of the moment for mass