That strikes me as you are given an expression containing some $f(t)$, and the first 3 cases give you an explicit function definition for $f$, while in the last you are to use a general function. For example, suppose in a Calc I course, the student is instructed that for each given $f(t)$, that are to compute:
$$\frac{d}{dt}\left(g^n(f(t)) \right)$$ and so they would do the following:
First, the student would find via the power and chain rules:
$$\frac{d}{dt}\left(g^n(f(t)) \right)=ng^{n-1}(f(t))\cdot f'(t)$$
i) $$f(t)=1+t^2$$
$$\frac{d}{dt}\left(g^n(1+t^2) \right)=ng^{n-1}(1+t^2)\cdot(2t)$$
ii) $$f(t)=2-t+3t^2$$
$$\frac{d}{dt}\left(g^n(2-t+3t^2) \right)=ng^{n-1}(2-t+3t^2)\cdot(6t-1)$$
iii) $$f(t)=4+t$$
$$\frac{d}{dt}\left(g^n(4+t) \right)=ng^{n-1}(4+t)\cdot(1)$$
iv) $$f(t)=p(t)$$
$$\frac{d}{dt}\left(g^n(p(t)) \right)=ng^{n-1}(p(t))\cdot p'(t)$$