St. deviation between groups

#1
My professor gave us this formula:

https://ibb.co/5WDvNHK

There are two groups, trying to figure out and justify the equation.

Mean for x1: 49.974
Mean for x2: 45.02
st. dev 1: .25
st. dev 2: .46

Is my math tracking? Feel like I'm missing something. Shout out to anyone willing to help on a friday night.