Calculating Time for Javelin Throw Angle Change

[Cheddar]

Homework Statement

In the javelin throw, the javelin is launched at a speed of 29m/s at an angle of 36degrees above the horizontal. As the javelin travels upward, its velocity points above the horizontal at an angle that decreases as time passes. How much time is required for the angle to be reduced to 18degrees?

Homework Equations

I can't find anything nor have we had any problems like this before.

The Attempt at a Solution

I'm sorry to say I can't even begin this problem. Anything that would point me in thr right direction would be great.

 

[tms]

Figure out the vertical speed from the initial speed and the angles. Then use the kinematics equations to find out when the vertical speed would decrease to the speed you calculated.