Find the partial derivative of (x*y) / (2+x)(4+y) with respect to x...

I know the answer is supposed to be

2y / (4+y)(2+x)^2

I have used Maple's tutor function, but still don't get it... I think I need to know what rules to apply and do I do anything to the equation before I start to differentiate?

Simon DK, thanks.