Let f be a twice differentiable function on (1,6). If f(2)=8, f^′(2)=5, f^′(x) ≥ 1 and f^′ ′(x) ≥ 4, for all x ∈(1,6), then:

Let $\displaystyle f$ be a twice differentiable function on $\displaystyle (1,6)$. If $\displaystyle f(2)=8, f^{\prime}(2)=5, f^{\prime}(x) \geqslant 1$ and $\displaystyle f^{\prime \prime}(x) \geqslant 4$, for all $\displaystyle x \in(1,6)$, then :