ball is stationary, hence the sum of forces has to be 0
draw a free body diagram, you should include the forces of tension, gravity and F
now, sum of forces vertically gives
Tcos35 = mg
so T = mg/cos35
sum of forces horizontally gives
Tsin35= F
so F = mgsin35/cos35
which is closest to B (g = 9.8, m = 20)