Calculating speed of the rotor with slip
This is pretty straight forward. The slip= (ws-wr)/ws,
where ws= 1000 rpm at 50 Hz and 1200 at 60 Hz ,
wr is the speed of the motor ,
wr at 50 Hz = 1000(1-2.2%) = 978 rpm,
wr at 60 Hz = 1200(1-2.2%) = 1173.6 rpm