Magnetic Field in a Toroid?

A toroid having a square cross section, 5.00 cm on a side, and an inner radius of 15.0 cm has 500 turns and carries a current of 0.800 A (It is made up of a square solenoid bent into a doughnut shape) What is the magnetic field inside the toroid at (a) the inner radius and (b) the outer radius?