[单选题]
A 1500-kg car traveling at 90.0 km/h east collides with (0y z1tkt e5 jy))ttwia 3000-kg car tr0+jp++ o 8jjiuy rngj2aveling at 60.0 km/h south. The two cars stick togetheij jjr + jg2+y+p0onu8r after the collision. (See Fig. 7-1.) What is the speed of the cars after collision?