The expression is given by some fixed costs (5 dollars),
and by some costs depending on how many pages there are (2 dollars and 15 cents).
Therefore for one page we have
$$5 + 2.15$$
for two pages we have
$$5 + 2.15 + 2.15$$
and for p pages we have
$$\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }\mbox{ }p\\
5+\overbrace{2.15+2.15+...+2.15+2.15}$$
or similarly
$$5+2.15p$$
If we evaluate this for 28 pages we have
$${\mathtt{5}}{\mathtt{\,\small\textbf+\,}}{\mathtt{2.15}}{\mathtt{\,\times\,}}{\mathtt{28}} = {\frac{{\mathtt{326}}}{{\mathtt{5}}}} = {\mathtt{65.2}}$$
.