Question 62052
{{{drawing( 300, 300, -10, 10, -14, 14,

  triangle( -3, -9, 8, -9, -3, 12 ))}}}
The base of the triangle is 8. The bottom left angle is 60 degrees. You want the know the opposite side.
tan(60 degrees) = x/8
8*tan(60 degrees) = x
The lamp post is about 13.86 feet.