According to the question,
Total number of blue balls in the bag = (x + 5 + x + x + 1) = (3x + 6)
According to the question,
\(\left\{{^xC_2}/{^{(3x+6)}C_2}\right\}=\frac{1}{35}\)
\(Or, \frac{x(x – 1)}{(3x + 6)(3x + 5)} = \frac{1}{35}\)
Or, 35x² – 35x = 9x² + 33x + 30
Or, 26x² – 68x – 30 = 0
Or, 26x² – 78x + 10x – 30 = 0
Or, 26x(x – 3) + 10(x – 3) = 0
Or, (26x + 10)(x – 3) = 0
Since, number of balls cannot be negative
Therefore, x = 3
So, the correct option is (D) : 3.