Hard problem on the chain rule for multivariable function ??

Hi ..

this is a problem from old exam ..

am lost .. i cant do anything!

i know the chain rule for F(x,y) where x=g(s,t) and y = h(s,t)

or for f(x,y,z,...) and x=g(s,t,...) y = h(s,t,....) and z=m(s,t,....) .. etc

what am gonna to said as am good ! (Nod)

but am lost at this (Headbang)

Problem :

Let F(s,t) be a differentiable function, let G(x,y) = F(x+y,xy),

calculate G_x(2,3) and G_y(2,3) if F_s(2,3)=1, F_s(5,6)=1

and F_t(2,3) = 4 and F_t(5,6) = 7

G_x = differentiating G with respect to x

F_t = differentiating F with respect to t

and so on..