In this question calculate speed of s2 sheep wrt s1 but in answer it give in only x direction why it not calculate whole speed i give my doubt in image also

A sDaceship S, leaves the Earth along the positive x-direction. Another spaceship S, also leaves the earth along the direction which makes an angle 60° with x-axis. The speeds of S, and S, are measured as 0.6c and 0.9c respectively by an observer on the earth. Find the speed of S, are measured by an observer in S,. (in terms of c)