Take into account that the vertical final velocity of the projectile is given by:
Now, consider that at the peak of the trajectory, the vertical final velocity is zero. Moreover:
Then, by solving for y into the equation for vy^2, you obtain:
where g = 9.8m/s^2 is the gravitational acceleration constant.
By using the given values for the angle and vo you obtain for the height of the peak y:
Hence, the height of the peak of the projectil trajectory is approximately 40.36 m