Recoil of astronaut pushing a tool

[Avis]

Homework Statement

An astronaut stranded in space throws a 0.70kg tool backwards at -12.0m/s in order to return to her spaceship. If she and her spacesuit together have a total mass of 90kg, how fast and in what direction is she moving after throwing the tool?

So
Et=Et

I'm not sure what to use. It has to be one that uses mass and velocity, I am just not sure.

 

[Dr.D]

Look at conservation of momentum.

 

[Avis]

Got it, thanks. All I ususally need is something to jumpstart my brain.