28 Calculați media aritmetică a numerelor x şi y, unde: a x = 2√27+3√12-5√48 +2√147; b x=2√√63-√252+3√28-√175; c x= 4√27+5√72-7√32-6√75; x=5√700-2√200+3√567 d +4√50; y = 4√12-3√75+11√108; y=√18+√√847-2√112-5√8; y=3√128 +6√108-8√18-10√27; y = 2√162+11√√28-9√8-3√63.​