Assuming the lightpole is the lighting source for the man's shadow and assuming the light is at the top of the light pole. Also assuming that we know the man's high, a parentheses was entered instead of a number so I am not sure what that means. But let's assume the man is 6 ft tall. We can then calculate the ratio of the hypotenuse (line from top of man's head to the tip of his shadow) to the length of the shadow. But before we do that we must figure out the length of the hypotenuse. The hypotenuse can be calculated using Pythagora's theorum (a squared + b squared = c squared) which in this case is 6*6 + 8*8 = 100. So the length of the hypotenuse is the square root of 100 or 10. So now we can get the ratio by dividing hypotenuse (10) by length of shadow (8). Which gives us 1.25. So now we can multiply 20 * 1.25 which gives 25 for the hypotenuse from the tip of the shadow to the top of the light post. We can once again turn to PG to solve the problem we 20 squared + x squared = 25 squared or 400 + x squared = 625... so 625-400=225... so the square root of 225 is 15ft.
