Given that the angle is 25 degrees, we shall apply cosine rule to solve this question. c^2=a^2+b^2-2abcosC thus plugging the values we get: 15^2=x^2+20x^2-40xcos25 x^2-36.252x+175=0 thus solving the quadratic using quadratic formula we obtain: x=[36.252+/-√614.208]/2 x=5.7 km or 30.5 km
