.After making his first deposit, Paul has $758 in his checking account. The next month, the balance is $836. The balance after the third month is $914.

Using liner sequences & function

Step-by-step explanation:

This is the way I understand the question.  I hope it makes sense.

    n

     ∑ (P + 78n)                P = the initial depost which is 758

   n = 0

     so when n = 0       the sum equals P   or  758        because 78(0)  =  0

     so when n = 1       the sum equals P+78(1)       =     758 + 78     =  836

     so when n = 2       the sum equals P+78(2)     =     758 + 156    =  914