Correct Answer  Option 3 :
\(\frac{2m(v+u)}{t}\)
The correct answer is option 3) i.e. \(\frac{2m(v+u)}{t}\)
CONCEPT:

Elastic collision: Elastic collision is a phenomenon where the collision of objects takes place such that the total linear momentum and kinetic energy of the system are conserved.
EXPLANATION:
 Since this is an elastic collision, linear momentum is said to be conserved.
As the ball moves forward and the plate moves towards it, the relative velocity of ball = v  (u) = v + u
After the collision, the relative velocity of the ball =  (v+u) = v  u
From Newton's second law of motion, \(F = \frac{m\Delta v}{t}\)
\(\Rightarrow F = \frac{m[(v+u )(vu)]}{t}\)
\(\Rightarrow F = \frac{2m(v+u )}{t}\)