`12)`
`3sqrt3(3+2sqrt6-sqrt33)`
`=3sqrt3.3+3sqrt3.2sqrt6-3sqrt3.sqrt33`
`=9sqrt3+6sqrt(3.6)-3sqrt(3.33)`
`=9sqrt3+6sqrt(3^2 . 2)-3sqrt(3^2 . 11)`
`=9sqrt3+18sqrt2-9sqrt11`
`13)`
`sqrt2(sqrt8-sqrt32+3sqrt18)`
`=sqrt(2.8)-sqrt(2.32)+3sqrt(2.18)`
`=sqrt(4^2)-sqrt(8.8)+3sqrt(6.6)`
`=4-8+18=14`
`14)`
`(5sqrt6-4sqrt10+7sqrt30):sqrt2`
`=(5sqrt6-4sqrt10+7sqrt30). 1/(sqrt2)`
`=(5sqrt6)/(sqrt2)-(4sqrt10)/(sqrt2)+(7sqrt30)/(sqrt2)`
`=5sqrt3-4sqrt5+7sqrt15`
`15)`
`(5sqrt3+3sqrt5):sqrt15`
`=(5sqrt3+3sqrt5) . 1/(sqrt15)`
`=(5sqrt3)/(sqrt15)+(3sqrt5)/(sqrt15)`
`=sqrt5+sqrt3`