Hypothesis Testing need steps

two samples of data determine if u can be 99% sure that company A makes more money than Company B

Co A Co B
mean 55,000 52,000
Std Dev 5,000 3,000
Sample size 200 400

I started out with z= 55,000-52,000
-----------------
V 5,000(2) + 3,000(2)
--------- ---------
200 400
Then, I get stuck?????? What do I do next to arrive at my answer?