Solution:

Simplifying the given expression:

Step 1: Simplify fractions within the brackets first.

- 6/11 x 4/7 = 24/77
- 9/12 x 4/3 = 3/4 x 4/3 = 1

Therefore, the expression becomes:

- 24/77 - 1 x (7/8 x 64/21)

Step 2: Simplify the multiplication inside the brackets.

- 7/8 x 64/21 = 448/168 = 56/21 = 8/3

Therefore, the expression becomes:

- 24/77 - 1 x 8/3

Step 3: Simplify the multiplication.

- 1 x 8/3 = 8/3

Therefore, the expression becomes:

- 24/77 - 8/3

Converting the fractions into like fractions:

Step 1: Find the LCM of 77 and 3, which is 231.

Step 2: Convert the fractions into like fractions with the denominator 231.

- 24/77 x 3/3 = 72/231
- 8/3 x 77/77 = 616/231

Therefore, the expression becomes:

- 72/231 - 616/231

Subtracting the fractions:

- 72/231 - 616/231 = -544/231

Therefore, the final answer is -544/231.

Answer: -544/231.

= (6/11×4/7)-(9/12×4/3)(7/8×64/21)
=(24/77)-(8/3)
=(72/231)-(616/231)
=-534/231
=-2.3116883117