Can someone give me a hint or the start of a possible proof for the following theorem:
A function $f: \mathbb{N}^r \rightarrow \mathbb{N}$ is primitive recursive if and only if there is a primitive recursive function $t:\mathbb{N} \rightarrow \mathbb{N}$ and a $t(n)$ time bounded Turing Machine $M$ that computes the function $f()$.
Any help will be much appreciated!!