An explorer is caught in a whiteout (in which the snowfall is so thick that the ground cannot be distinguished from the sky) while returning to base...

An explorer is caught in a whiteout (in which the snowfall is so thick that the ground cannot be distinguished from the sky) while returning to base camp. He was supposed to travel due north for 4.8 km, but when the snow clears, he discovers that he actually traveled 7.8 km at 50° north of due east. (a) How far must he now travel to reach base camp?