Let f:[1, ∞) →[2, ∞) be a differentiable function. If 10 ∫_1^x f( t ) dt =5 x f(x)-x^5-9 for all x ≥ 1, then the value of f(3) is:

Let $\displaystyle f:[1, \infty) \rightarrow[2, \infty)$ be a differentiable function. If $\displaystyle 10 \int_1^x f(\mathrm{t}) \mathrm{dt}=5 x f(x)-x^5-9$ for all $\displaystyle x \geqslant 1$, then the value of $\displaystyle f(3)$ is :