Hi there, could you please help with this? Thank you in advance!

9. (a) Let MR(q) and E be the marginal revenue and the point elasticity of demand re- spectively. Show that MR(q) = p 1 where p = p" P(q). E (b) For any p > 0, use (a) to write down the corresponding necessary and sufficient condition (in terms of MR(q) ) for the demand to be (i) elastic (ii) inelastic (iii) unit elastic (c) Given the demand function q"(p) = 80 - 5p. (i) Find MR(q) and E. (ii) Verify the formula in (a). What is the price when the demand is unit elastic