the answer is on the 2nd picture, thank you!

A company begins and ad advertising for its product. The percentage of people in the city who got to see the ad t days from the start of the ad campaign is: 16. f(t) = 1 - e-0.06 How long will it take until the ad reaches 50% of the people in town. 17. The advertising response N(a), where N is the number of items sold and a is the amount spent on advertising in thousands of dollars, is N(a) = 1000 + 400ln(a) for a > 0 a) How many units were sold after spending $4000 in advertising? b) How much money should be spent in order to sell 1500 units? 16. 11.55 days 17. a) about 4,318 units, b) 3.490 thousand dollars, or $3,400