Let f, g : R R be two real valued functions defined as f(x) = \left\{ {\matrix{
{ - |x + 3|} & , & {x < 0} \cr
{{e^x}} & , & {x \ge 0} \cr
} } \right. and g(x) = \left\{ {\matrix{
{{x^2} + {k_1}x} & , & {x < 0} \cr
{4x + {k_2}} & , & {x \ge 0} \cr
} } \right., where k₁ and k₂ are real constants. If (gof) is differentiable at x = 0, then (gof) ( 4) + (gof) (4) is equal to :