a) All forces acting on mass 2 are:
gravity, force from the student and force from the string 2.
Gravity is `m_2*g` , the force F from the student is given and the force from the string is equal in magnitude to the tension in string 2, `T_2` , according to the third Newton's Law.
Since mass 2 is in equilibrium,
`m_2*g + F = T_2`
Letting g = 10 N/kg,
`T_2 = 40 N + 6*10 N = 100 N`
Using the same reasoning, the equation for the forces acting on mass 1 is
`m_1*g + T_2 = T_1` , where `T_1` is the tension in the string 1.
Therefore `T_1 = 100 N + 4*10 N = 140 N`
The tension in the string 1 is 140 N and the tension in string 2 is 100 N.