how do i do 2 and 3?

(2) A company is selling widgets. If they sell 20,000 widgets they make a profit of a thousand dollars. At this amount of sales, the company's marginal profit is 1 cent per widget. (a) Use approximation by increments to estimate the company's profit if it sells 22,000 widgets. (b) Approximately how many more widgets (beyond 20,000) would they have to sell to make a profit of $1,050? (c) (Optional bonus) Explain why there must have been some number n