The effort applied : 200 N
<h3>Further explanation</h3>
Equilibrium rotation

F₁.d₁-F₂.d₂=0
F₁.d₁=F₂.d₂
F₁=500 N
d₁=0.5 m
d₂=1.75-0.5=1.25 m

Explanation:
Let x and y are two unknown resistors. When they are connected in series their equivalent resistance is 15 Ω. When they are connected in parallel, their equivalent resistance is 3.3 Ω.
For series combination,
......(1)
For parallel combination,
....(2)
We need to find the resistances of these resistors. Solving equation (1) and (2) we get :
x = 0.29 and y = 14.7
Hence, the resistances of these resistors are 0.29 ohms and 14.7 ohms.
Well I think B hope this helps