# Simple but nice

Calculus Level 1

${F(x)} = {f(x)g(x)h(x)}$

The above equation is true for all real $$x$$, where $$f(x)$$, $$g(x)$$ and $$h(x)$$ are differentiable functions at some point $$a$$.

Given $$F '(a) = 21 F(a), f '(a) = 4f(a), g'(a) = -7g(a), h'(a) = kh(a)$$. Find $$k$$.

×