Question

The resultant of two forces of magnitiude f and 2f can be a)less thab f b)more than 3f

Answer 1

Considering no other force is applied on the body (absence of gravitational and normal force), the force can neither be greater than 3f nor be smaller than f.
If the forces are exactly opposite of each other, the resultant force will be f or -f(depending on the directions of given force)
If they are applied from the same direction, the resultant force will be 3f or -3f(depending on the direction)