Dan and Kate used two different treadmills to exercise. The total distance walked between them was 3.7 miles. How do you state what quantity the variable x represents and express the second quantity in terms of x?
Since we are not given any reason to do otherwise, we can define
Now, to find an expression for Kate's walk. You can do it this way:
Since the total distance is 3.7 miles, it must be that
There is your second expression. The distance Kate walks is