For a given interest​ rate, simple interest varies jointly as the principal and time. If ​$2000 left in an account for 6 years earned interest of ​$960, then how much interest would be earned in 7 ​years?

Answer 1

i = kpt, so if p is the same,
i/t = pk is constant.
Thus, you want i such that

960/6 = i/7

That is, since 7 is 7/6 as big as 6, the interest will be 7/6 * 960