physics
posted by help on .
The engines of a 1.20 x 10^5 N rocket exert an upward thrust of 2.00 x 10^5 N for 1.50 minutes upon lift off.
What is the impulse exerted on the rocket?
What is the velocity of the rocket at the end of the 1.50 minute period?

impulsr=force*time=2E5*90 Nseconds
changevelocity=impulse/massrocket 
I don't understand where the 90 comes from