1. The problem statement, all variables and given/known data
A placekicker must kick a football from a point 36.0 m (about 40 yards) from the goal, and half the crowd hopes the ball will clear the crossbar, which is 3.05 m high. When kicked, the ball leaves the ground with a speed of 23.0 m/s at an angle of 46.0° to the horizontal.
I have completed the problem correctly but was told to find time by t= delta x / (vi *costheta)
Where is this equation derived from is what i'm asking?