Find the value of the combination 21C3

Kerion has a beaded necklace business. she can make 12 necklaces is 2 hours. how long will it take her to make 9 necklaces?

Graph the line y=4/3 x+1 . use the line tool and select two points on the line.

Use mathematical induction to prove the statement is true for all positive integers n, or show why it is false. 1^2 + 4^2 + 7^2 + + (3n - 2)^2 = [n(6n^2-3n-1)/2]