c) (24/√20+80/8√5+√20/20)+(12/8√5-2/√5-35√5/14)=
=24/2√5+20/2√5+2√5/20+3/2√5-2/√5-5√5/2=
=24√5/10+20√5/10+√5/10+3√5/10-4√5/10-25√5/10=
=24√5/10+20√5/10+√5/10+3√5/10-4√5/10-25√5/10=
=19√5/10
d) (30/√6-5√6/2+√6/2)-(√6/2+16/2√6-15/√54+8√6/12)=
= 30/√6-5√6/2+√6/2-√6/2-8/√6+15/√54-8√6/12=
= 30√6/6-15√6/6-8√6/6+5/√6-4√6/6=
=8√6/6=4√6/3