another way of thinking of the chain rule is

If y = y (u) and u = u(x)

Then dy/dx = (dy/du)(du/dx)

For y= u (u^2 + 3) ^3 where u = (x+3)^2

dy/du = (u^2 + 3) ^3 + 6u^2 (u^2 + 3) ^2 (Product rule)

dy/du = [(u^2+3)^2] [7u^2 +3]

du/dx = 2(x+3)

dy/dx = 2[(u^2+3)^2] [7u^2 +3](x+3)

Normally we would now convert u to (x+3)^2 but we only need the derivative when x= -2 . Note if x= -2 then u = 1

substitute into the above eqn.