Please help me with the following question:

A sculptor commissioned to design a monument for the long reach city council, has chosen a parabolic shape that stand 15m high with supports at 45° as shown in the diagram. For aesthetic reason the sculptor chooses the shape given by the function

Y = 15 -x²

π (pie)

ie. y equals 15 minus x² over π (pie)

Find the length of the support beam marked A. Provide justification for your answer.