Consider the following data of total revenue (TR) and total cost (TC) of a firm.

\begin{tabular}{|l|c|c|c|c|c|c|c|c|}
\hline
Output & 0 & 1 & 2 & 3 & 4 & 5 & 6 & 7 \\
\hline
TR & 0 & 220 & 400 & 540 & 640 & 700 & 720 & 700 \\
\hline
MR & & & & & & & & \\
\hline
TC & 120 & 270 & 370 & 440 & 540 & 670 & 830 & 1020 \\
\hline
MC & & & & & & & & \\
\hline
Profit & & & & & & & & \\
\hline
\end{tabular}

a. Calculate marginal revenue (MR), marginal cost (MC), and profit in the table above, and find the equilibrium level of output from both the TR-TC approach and the MR-MC approach.

b. Plot the values of TR, TC, and profit on a graph and find the equilibrium point.