I agree with GingerAle.
This joke isn't racist, it's a pun. These days, many people are trying to point out everything as racist. They're like, "That's so racist!" or "Are you being racist?" in a loud voice. As long as you are not insulting Russians just because they are Russians, you are fine. Your friends just want something to make fun of. Ignore their comments and they'll get over it (if they already haven't).
It's been a while since I've posted a math explanation...
Alright, you'll have to subtract those two equations, but you have to make one term (with variable) the same.
Let's allow both equations to have 3x.
3x+2y=16 already has 3x inside, so leave it alone.
So for x-y=-3 to have 3x, you multiply 3 to every term in that equation.
Let's subtract now.
-5y = -25
So we have -5y = -25
Divide both sides by -5 and you get y=5.
Plug 5 for y in any equation to get x. I'll use the first one.
x = 2
So x=2, y=5.