Values of a linear cost function are in Table $1.27 .$ What are the fixed costs and the marginal cost? Find a formula for the cost function. $$\begin{array}{c|c|c|c|c|c}\hline q & 0 & 5 & 10 & 15 & 20 \\ \hline C(q) & 5000 & 5020 & 5040 & 5060 & 5080 \\\hline\end{array}$$