This is the concept of arithmetic sequence. To get the recursive formula that models the total amount Jobie has in her account we use the arithmetic formula given by: an=a+(n-1)d where: an=nth term a=first term n=number of terms d=arithmetic difference in our case a=$325 d=$10 the initial amount was: a0=325 the amount in the second month will be: a1=325+10 the amount in the thrid month will be: a2=a1+10 after n months the we shall have: an=a_(n-1)+10 hence the recursive formula will be: an=a_(n-1)+10 where: n=1,2,3,4,..., a0=325