Son, this problem can only be solved by equations, which mainly tests your ability to do equations. You can set the walking speed to x, so the walking time is 3.5/X, because the distance runs fast, so (1)3.5/3 divided by 4X is the running time, and the latter two thirds are jogging, so the jogging time is (2)3.5x2/3 divided by 2X. Then subtract the sum of (1)(2) from 3.5/X =35. The equation is (7/2x)-[(7/24x)+(7/6x)] = 3549/24x = 35x = 7/120, so the walking time is 3. Is that clear enough? Typing is not easy. Take it.