I know Projectile motion is physics in nature but i am having problems with the mathematical mechanics and any help would be greatly appreciated,

A fighter pilot blows up a artillery dump. Diving at an angle of 53degrees below the horizon, the pilot releases a bomb at an altitude of 750m. The bomb hits the target 5.0s after being released.

What is the velocity of the bomber?

So i enter this into the equation d= vt - (1/2)gt^2 yet i get a negative number which to me doesnt make sense.