City B is 10 miles downstream from city A and on the opposite side of a river half a mile wide. Mary will run from city A along the river for 6 miles, and then swim diagonally (i.e., along a straight line) across the river to city B. If she runs at 8 miles per hour and swims at three miles per hour she will reach City B after hours. Assume that the current is negligible.
Note that unless otherwise specified WeBWorK expects your answer to be within "one tenth of one percent" of the "true answer" which is the answer it has been given by the author of the problem. Practically speaking this means you should specify at least 4 digits total (including any before the decimal point). To be safe, you want to compute your answer with your calculator much more accurately.
Hint: Draw a picture and apply the Pythagorean Theorem;