Walker, Halliday & Resnick — Maxwell's Equations; Magnetism of Matter: Problem 12

12 Assume the average value of the vertical component of Earth’s magnetic field is \(43\text{ }\mu\text{T}\) (downward) for all of a certain land region of the United States, with an area of \(2000\text{ km}^2\). What then are the (a) magnitude and (b) direction (inward or outward) of the net magnetic flux through the rest of Earth’s surface (the entire surface excluding Arizona)?