100rs^2t^2 + 24r^2s^2t^3 - 122r^3s^2t^2
Let's see... what do all three of these terms have in common?
They're all divisible by 2, for starters. And they each contain an r, an s, and a t.
So let's take out those.
2rs^2t^2(50 + 12rt - 61r^2)
Because when you multiply the 2rs^2t^2 by each of the terms inside the parenthesis, (distributing), you should get the initial terms you began with. (Exponents are added when you multiply them together. So r^3 times r^2 would be r^5, for example.)
This should be correct! I'm in a rush so I didn't get to fully check it. Good luck!