For low speeds, the drag force is proportional to the velocity. So we can write the following proportion:
[tex]15 m/s:240 N = 25 m/s:F[/tex]
where F is the drag force in the second situation. By solving the proportion, we find that the drag force at v=25 m/s is
[tex]F= \frac{(240 N)(25 m/s)}{15 m/s}=400 N [/tex]