4/9÷[5/6-(1/6+1/3)]
=4/9÷[5/6- 3/6]
=4/9×3
=4/3
1/15*(1/3+1/12)
=1/15*5/12
=1/36
1/4÷(3-5/13-8/13)
=1/4÷(3-1)
=1/8