Ignoring the thickness of the board, it looks like an application of the sine function.
Let's see what you get.
Hi triknobchin,
The 20 foot board will be the hypotenuse of a right triangle formed by the board, the road, and the 1 foot block.
The angle of elevation will be the angle formed where the board meets the highway.
You have opposite side and hypotenue. Use inverse sine to find the angle of elevation.