Help Please!

I am stranded, stationary, in space, but near to my spacecraft. I detach my 30kg oxygen cylinder, and fling it away from the spacecraft with a speed of 3.0ms−1. If my mass (without the cylinder) is 80kg, how fast will I travel in the other direction towards my spacecraft?

Again what have you tried?

mv before = mv after
(110 * 3) = 80v
330/80 =v
v= 4.1ms-1 however this was wrong.

I am stranded, stationary, in space, but near to my spacecraft. ....

Read the question properly

it changes direction so it would be a negative?