23. The figure shows a cross section of a long cylindrical conductor of radius a = 4 cm containing a long cylindrical hole of radius b = 1.5 cm. The central axes of the cylinder and hole are parallel and are distance d = 2 cm apart; current i = 5.25 A is uniformly distributed over the tinted area. The magnitude of the magnetic field at the center of the hole is(A)7.6 μT(B)15.3 μT(C)24.7 μT(D)35.9 μT(E)51.8 μT