A building has two storeys with unequal heights. From an observation point on the ground ${50\ {\rm ft}}$ from the bottom of the building, the angle of elevation to the bottom of the second storey is $21$ degrees, and the angle of elevation to the top of the second storey is $36$ degrees. Find the height of the second storey. Round your answer to two decimal places if needed. The height of the second storey is .