$4.$ Classify the $15$ items listed below into one of the following six categories:

a$)$ Assets b$)$ Liabilities c$)$ Equity d$)$ Revenue e$)$ Expense f$)$ Off$-$balance$-$sheet activities

$(1)$ Service fees charged on deposit accounts, $(2)$ Retail CDs$,(3)$ Surplus and paid$-$in capital, $(4)$ Loan commitments, $(5)$ Consumer loans, $(6)$ Federal funds sold, $(7)$ Swaps, $(8)$ Interest on municipals, $(9)$ Interest on NOW accounts, $(10)$ NOW accounts, $(11)$ Commercial letters of credit, $(12)$ Leases, $(13)$ Retained earnings, $(14)$ Provision for loan losses, $(15)$ Interest on U$.$S$.$ Treasury securities