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 $\displaystyle p=\frac{20-q}{0.5} $
and$\displaystyle q=20-0.5p$
so $\displaystyle p \cdot q = [\frac{20-q}{0.5}]\cdot [20-0.5p]$

Is that right?