From the end of the horizontal line draw a vertical line (so that a right-angle is formed with the horizontal) until it reaches the angle line.
You should now have a right-angled triangle to work with. We know that the hypotenuse is 500m and the angle is 20 degrees. To find the height label the vertical line h and note this opposite the 20degree angle.
We now have an angle and the hypotenuse while needing to find the opposite. Can you recall a trig ratio to use in this situation