A plane flying with a constant speed of 14 kmmin passes over

A plane flying with a constant speed of 14 km/min passes over a ground radar station at an altitude of 13 km and climbs at an angle of 50 degrees. At what rate, in km/min is the distance from the plane to the radar station increasing 4 minutes later?

__________?

c² = a²+b²-2ab cos (90+50)deg c² = 13² + (4*14)² - 2*13*4*14 *cos 140 ==>c=66.5 c\' = (1/2c)(2bb\' - (2a cos 140)b\') =(14/133)(2*4*14 -2*13*cos140) =13.886km/min