So,
We could write the following equation, where "x" is the number of miles travelled.

If we solve this equation, the first thing we're going to do is to let all "x terms" in a side of the equation and all the numbers in the other side. If "25" is summing in a side, it will change its sign when we pass it to the other side. Like this:

Now, we substract the numbers above and get:

Now, if 0.35 is multiplying "x", we are going to pass this number to divide the amount in the other side:

Therefore, Ken travelled 77 miles.