Let "d" be the unknown one-way distance, in miles. Then the average speed biking up wasmph; the average speed of return trip was mph. The difference in average rates was 2 mph - = 2 mph. It is your basic equation. To solve it, first simplify the equation - = 2, or - = 2. Next, multiply both sides by 35. You will get (2d)*7 - (2d)*5 = 70 14d - 10d = 70 4d = 70 d = = 17.5 miles. ANSWER