angle at which the ball moves after the collision

a ball moving at a speed of 6.5 m/s strikes a stationary ball of the same mass. the two balls undergo an elastic collision. after the collision, the first ball moves at an angle of 37º relative to the original line of motion.
 
find the angle at which the second ball moves after the collision.
 
 
how do you do solve this? using the sine or cosine law gives me two unknowns...
 
 
 
 
 

for the case of an equal mass elastic collision, the angle between the exit velocities is 90 degrees.  hence second ball moves at an angle 90 - 37 = 53 degrees with respect to the original line of motion.