So, in this equation you're just plugging in I'm pretty sure. So x is -2 which is pretty self explanatory.. & y is 2. If you plug them in like so, your answer will turn out to be -6.
6(-2)+3(2)=-6
-12+6=-6
The answer should be -6 not -9.. so that was most likely a typo I'm pretty sure because the answer would not be correct as -9.