Answer:
Assets = Liabilities + Stockholders' Equity
(a) $50,000 (AR) $50,000 (RE)
(b) $42,000 (C) - $42,000 (AR)
(c) $35,000 (Equip) $35,000 (NP)
(d) -$5,000 (C) -$5,000 (C)
total $80,000 $35,000 $45,000
on (b), assets total amount doesn't change, one account replaces the other