So with 8% interest, Jim will have to pay 8% more each year. For the first year we need to multiply 210 with 1.08 to find the amount that Jim would have had to pay to his sister if he had gotten an 8% interest for 1 year. Every time the year increases we need to multiply the previous number with 1.08 because we are looking for the 8% increased value of the previous one, therefore our equation is:
P(t) = 210*(1.08)^t --> (t=time in years, P(t)=amount of money Jim need to pay back with respect to time)
Since Jim gets an 8% interest for 7 years we have to put in 7 for t.
