The distance between the two fires can be found using the Law of Cosines. For ΔABC in which sides 'a' and 'b' are given, along with angle C, the third side is ...
c = √(a² +b² -2ab·cos(C))
The angle measured between the two fires is ...
180° -(69° -35°) = 146°
and the distance is ...
c = √(11² +21² -2(11)(21)cos(146°)) ≈ √945.015
c ≈ 30.74
The straight-line distance between the two fires is about 30.7 km.