Find the total revenue(TR) function if the demand equation is q = 20-0.5p.How much must be sold to maximize TR? What is Marginal revenue (MR) at this output?

anyone know how to work this out?

I know MR= TR'.

And TR = pq

so does that mean p=\frac{20-q}{0.5}
and q=20-0.5p
so p \cdot q = [\frac{20-q}{0.5}]\cdot [20-0.5p]

Is that right?