JEE Advanced 2020 Concept Recapitulation Test 4 Paper 2

A boy throws a ball at time t=0 with upward initial velocity =20m∕s, from the comer of the roof of a building, whose height above the ground is 25m. If the velocity of the ball is simply reversed after collision from the ground (magnitude remaining same), and the 3‌vd ‌ collision of the ball with the ground occurs at t=t1sec. What is the value of t1 ?