Alan is a software salesman. His base salary is $1600, and he makes an additional $40 for every copy of Math is Fun he sells. Let P represent his total pay (in dollars), and let N represent the number of copies of Math is Fun he sells. Write an equation relating P to N. Then use this equation to find his total pay if he sells 21 copies of Math is Fun. Equation: D=0 Total pay if Alan sells 21 coples: $] Х 5 ?