Notice that the angles of the right triangle are 40 and 50 degrees, with the 500 meter side adjacent to the 50 degree angle. Now, we can set up an equation: cos (50 degrees) = 500 / x. Use a calculator to find that the answer is 777.9.
To find the percentage out of a fraction you would divide 4÷5 to get 0.8, the decimal answer, then to turn that to a percent you would move the point two places to the right to get 80%.