What is marginal revenues and what is marginal cost
And how to find them to maximised profit

Read the homework help rules, and check back in with your attempts at answering the questions. In the meantime, a couple of hints...

Marginal revenue (and marginal cost) is the rate of change of the Revenue (and Cost) functions, at any output level q. For example, if R(q) is your Revenue function, then

R'(q) = \frac{dR}{dq}

Now think about your typical Rev and Cost curves, shown simultaneously on a standard XY plane. In what form does net profit appear on that graph? And with that in mind, what relationship would Rev's and Cost's derivatives have at the q-point of maximum profit?