What is the coefficient of $xy$ in the expansion of $(3x+(2y+1))^2$?
To expand this expression, I can use the binomial formula: $(a+b)^2=a^2+2ab+b^2$. In this case, $a=3x$ and $b=2y+1$. So, applying the formula, I get $(3x+(2y+1))^2=(3x)^2+2(3x)(2y+1)+(2y+1)^2$. I need to simplify this expression and find the term that has $xy$ in it. Expanding the squares, I get $9x^2+6x(2y+1)+4y^2+4y+1$. Multiplying out the middle term, I get $9x^2+12xy+6x+4y^2+4y+1$. The term that has $xy$ in it is $12xy$. The coefficient of $xy$ is the number that is multiplied by $xy$, which is 12. 