Thanks Chris,

This can be easily done by any good yr 9 student.

$$\\\boxed{(a+b)^2=a^2+2ab+b^2}\\\\

so\\\\

(3x+(2y+1))^2\\

=(3x)^2+2*3x*(2y+1)+(2y+1)^2\\

=etc\\\\

$The only term with xy is going to be $ \\

2*3x*2y=12xy\\

$so the coefficient of xy is 12$$$