（5分之4＋3分之8）÷4
=4/5÷4+8/3÷4
=1/5+2/3
=5/15+6/15
=11/15
21.5÷5分之2＋8.5÷5分之2
=（21.5+8.5）÷2/5
=30÷2/5
=75