`a) (3sqrt{2} + sqrt{6})sqrt{6 - 3\sqrt{3}}`
`= sqrt{2}(3 + sqrt{3}).sqrt{(12 - 6\sqrt{3})/(2)}`
`= sqrt{2}(3 + sqrt{3}).(\sqrt{(3 - \sqrt{3})^2})/(\sqrt{2})`
`= (3 + sqrt{3}).(3 - sqrt{3})`
`= 9 - 3`
`= 6`
`b) sqrt{31 - 8\sqrt{15}} + sqrt{24 - 6\sqrt{15}}`
`= sqrt{4^2 - 2.4.\sqrt{15} + 15} + sqrt{3^2 - 2.3.\sqrt{15} + 15}`
`= sqrt{(4 - \sqrt{15})^2} + sqrt{(\sqrt{15} - 3)^2}`
`= |4 - sqrt{15}| + |sqrt{15} - 3|`
`= 4 - sqrt{15} + sqrt{15} - 3`
`= 1`
