Help with this problem

(3√8 - 1/√3 - √18 )²

3√8 =
3 * √4 * √2 =
3 * 2 * √2 =
6√2

1/√3 =
√3 / 3

√18 =
√9 * √2 =
3√2

6√2 - (√3/3) - 3√2
3√2 - (√3/3)
(9√2 - √3) / 3

[(9√2 - √3) / 3]^2

[(9√2 - √3)(9√2 - √3) / (3 * 3)]

(81*2 - 9√6 - 9√6 + 3) / 9

(162 - 18√6 + 3) / 9

(165 - 18√6) / 9

3(55 - 6√6) / 9

(55 - 6√6) / 3

(3√8 - 1/√3 - √18 )² ,{ √8 = √(4.2) = 2√2 , √18 = √(9.2) = 3√2 }

= ( 3 . 2√2 - 1/3 . √3 - 3√2 )²
= ( 6√2 - 1/3 . √3 - 3√2 )²
= ( 3√2 - 1/3 . √3 )² , ( a - b )² = a² - 2ab + b²
= (3√2)² - 2 . (3√2) . (1/3 . √3) + (1/3 . √3)²
= 18 - 2√6 + 1/3
= 55/3 - 2√6

(3√8 - 1/√3 - √18)²
= (6√2 - 1/√3 - 3√2)^2
= (3√2 - 1/√3)^2
= 18 - 2√6 + 1/3
= 18 - 4.899 + 0.3333
= 13.101 + 0.333
= 13.434

(3√8 - 1/√3 - √18)²
= (3√8 - 1/√3 - √18)(3√8 - 1/√3 - √18)
= (72 - 2√6 - 36 - 2√6 + 1/3 + √6 - 36 + √6 + 18)
= 18 - 2√6 + 1/3
= 18 - 4.899 + 0.333
= 13.434

What exactly is the problem ?