`#2k12`

`19) |-(15)/6|-|3/(18)| . \sqrt {81} + \sqrt{9/(64)}`

`= 5/2 - 1/6 . 9 + 3/8`

`= 5/2 - 3/2 + 3/8`

`= 1 + 3/8`

`= (11)/8`

`20) \sqrt{0,36} . \sqrt{(25)/(16)} + |-3/4| . 0,(3)`

`= 0,6 . 5/4 + 3/4 . 1/3`

`= 3/5 . 5/4 + 3/4 . 1/3`

`= 3/4 + 1/4 = 1`

`21) (-2)^2 + |-3/2| . \sqrt{36} - 8/3 . \sqrt {9}`

`= 4 + 3/2 . 6 - 8/3 . 3`

`= 4 + 4 - 8`

`= 8 - 8=0`