`a, 4/15 xx 7/3+ 11/6 xx 4/15`
`= 4/15 xx (7/3 + 11/6)`
`= 4/15 xx (14/6 + 11/6)`
`= 4/15 xx 25/6`
`= (2 xx 2 xx 5 xx 5)/(3 xx 5 xx 2 xx 3)`
`= 10/9`
`b, 7/36 xx 25/9 xx 36/7 xx 18/5`
`= (7/36xx36/7)xx(25/9xx18/5)`
`= 1 xx (5 xx 5 xx 2 xx 9)/(9 xx 5)`
`=1 xx10`
`= 10`
a, 4/15x(7/3+11/6)=4/5x25/6=10/3
(7/36x36/7)x25/9x18/5=1x10=10