Amarginal benefit curve has a negative or a positive slope?

Afirm wants to hire a project manager (pm) at a salary of $100,000. 30% of pms have high ability, and 70% of pms have low ability. high ability pms generate $120,000 in revenue and low ability pms generate $80,000 in revenue. in addition to differences in productivity, high and low ability pms have different outside offers. if a high ability pm is not hired by the firm, she can work for another company at a salary of $80,000. if the low ability pm is not hired by the firm, she can work for another company for $70,000. high ability pms are also able to get a project management professional (pmp) certification at a cost of $1,000. low ability pms are unable to get a pmp certification (they would fail the test). the firm is not able to observe a pm’s ability, but is able to observe and verify whether or not the pm has a pmp certificate.(a) draw the extensive form of the game.expert answer