Let speed of bus be 'x' and speed of car be 'y'
Using the equation Distance/Speed=Time, we get two equations
180/x + 450/y = 12.......(1)
120/x + 510/y = 11.5.....(2)
Multiplying both equations on both sides by xy, we get
180y + 450x = 12xy.......(1)
120y + 510x = 11.5xy.....(2)
Simplifying the equations, we get x=40 km/h and y=60 km/h