suppose the demand function for q units for a certain item is

p=d(q)=100+(50/lnq),q>1

where q is in dollars

a) find the marginal revenue.

b)approximate the revenue from one more unit when 8 units are sold.

c)how might a manager use the information from part b?

As for this one, I figuared out that R'=50q^2+50/lnq+100

but I have no idea for part b and c