Kimberly owns a restaurant. She charges $3.00 for 2 eggs and one piece of toast, and $2.40 for one egg and two pieces of toast. How much does Kimberly charge for an egg? A piece of toast?

Use stokes' theorem to evaluate c f · dr where c is oriented counterclockwise as viewed from above. f(x, y, z) = xyi + 5zj + 7yk, c is the curve of intersection of the plane x + z = 8 and the cylinder x2 + y2 = 81.