To solve this problem, we can already start looking at which equation we can make, since we have all the data. To find the time it takes, we know that we will have to have the distance on the top and the speed on the bottom. That eliminates the bottom two options. But, since we know that the speedboat is moving against the current of the lake, that means we subtract x from the total speed, 70. That means that the answer to this problem is f(x) = [tex] \frac{25}{70-x} [/tex]
