I need help with another physics problem?

A projectile is fired at time t=0.0s, from point o at the edge of a cliff, with initial velocity components of v sub ox =60m/s and v sub oy= 800m/s. The projectile rises, then falls into the sea at point P. The time of flight of the projectile is 200.0s. What is the magnitude of the velocity at time t=15.0s.