The shadow is formed at a specific factor of the original image hence if a 5 feet tall man casts a shadow rhat is 4 1/3 feet long then a telephone pole casts a shadow that is 25.5 feet long must have a length
Because if you look at diagram x is vertical to angle FBC, and angle FEC and angle EBA are alternate interior angles so they are equal to each other, and AC is a straight line which means it equals to 180 degrees.