`a)`
`A =3sqrt8 - 2sqrt{18}+sqrt{20}`
`= 3sqrt{2^2}sqrt2 - 2sqrt2sqrt{3^2} + sqrt{2^2}sqrt5`
`= 6sqrt2 - 6sqrt2 + 2sqrt5`
`= 2sqrt5`
`b)`
`B = (3-sqrt3)/(sqrt3-1) - (2-sqrt2)/(1-sqrt2)`
`= ((3-sqrt3)(sqrt3+1))/((sqrt3-1)(sqrt3+1)) - ((2-sqrt2)(1+sqrt2))/((1-sqrt2)(1+sqrt2))`
`= ((3-sqrt3)(sqrt3+1))/(sqrt3^2-1^2) - ((2-sqrt2)(1+sqrt2))/((1^2-sqrt2^2)`
`= (3sqrt3+3-3-sqrt3)/2 - [-(2-sqrt2)(1+sqrt2)]`
`= (2sqrt3)/2 - [-(2+2sqrt2-sqrt2-2)]`
`= sqrt3 - (-sqrt2)`
`= sqrt3 + sqrt2
