Minimization problem

Minimization problem

Consider $ k_1/x = k_2/x + c $
Lets define a function $ f(x) = (ax+b)^2 (k_2/x + c) $
Given that $ k_1 > k_2 $ and $ a ,b, c >0 $
There exists a positive $x^*$ for which $f(x)$ attains the minimum value.
Find condition(s) for $x^* \geq x$