Experimental tests have shown that hammerhead sharks can detect magnetic fields. In one such test, 100 turns of wire were wrapped around a 7.0-m-diameter cylindrical shark tank. A. magnetic field was created inside the tank when this coil of wire carried a current of 1.5 A. Sharks trained by getting a food. reward when the field was present would later unambiguously respond when the field was turned on. 

a. What was the magnetic field strength in the center of the tank due to the current in the coil? 

b. Is the strength of the coil's field at the center of the tank larger or smaller than that of the earth?