The amount of commission...

The amount of commission earned by an online brokerage in a month C,(in hundreds of dollars) is a function of online advertising expenditure, a (in hundreds of dollars) so we write C=f(a).

a.What does the brokerage hope is true about the sign of f' (positive or negative).Why?

b.What does the statement f'(12)=1.4 mean in terms of advertising and commission?

c.Suppose that the company plans to spend about $1200 on advertising.If f'(12)=1.4, then should the company spend more or less on advertising?

a) he'll want f'(x) to be possitive since it means that the commision is increasing.
B) when 12 are spent in ads, the commision grows by 1.4
c)more i guess.