I got the wrong answer for this question, what equations do I use?

During an ice show a 60.0 kg skater leaps into the air and is caught by an initially stationary 65.0 kg skater. (a) What is their final velocity in meters per second assuming negligible friction and that the 60.0 kg skater's original horizontal velocity was 4.00 m/s? (Enter a number.) m/s (b) How much kinetic energy is lost in joules? (Enter a number.)