Basic Linear Problem Solving Qn.

Could somebody help me with this question?

Im not sure what to really do, as I'm finding myself with an extra unknown, and Im certain there's a easier method of solving this question.

Any help would greatly be appreciated.

Thank you.

**An aircraft used for fire spotting, flies from its base to locate a fire at an unknown distance, x km away. It travels straight to the fire and back, averaging 240km/h for the outward trip and 320km/h for the return trip. If the plane was away for 35min, find the distance, xkm. **