A model for advertising response is given by the function
N(a) = 1000 + 200 ln a, a ≥ 1,
Where N(a) is the number of units sold when a is the amount spent on advertising, in thousands of dollars.
a) How many units were sold after spending $1000 (a = 1) on advertising?
b) How many units were sold after spending $5000?
c) Graph the function.
d) How much would have to be spent in order to sell 2000 units?