Find mass of a rope pulled by a force

[Jahnavi]

Homework Statement

Homework Equations

The Attempt at a Solution

The force F exerted by the wall on the left end of the rope will make an angle 30° with the vertical . If we do the force balance ,

F sin30° = 20
Fcos30° = Mg

This gives M = 2√3 Kg . This gives 3.5 Kg . But answer given is option 4) . What is the mistake ?

Edit : There is a mistake in the answer key . Correct option is 3) .

 

[Gene Naden]

Your force balance is correct, as is your final result.