To solve this equation, we will first distribute the numbers and simplify both sides:

21(4x/7 - 2/3) + 3/4 = 3(x + 1/4) + 9x - 14
84x/7 - 42/3 + 3/4 = 3x + 3/4 + 9x - 14
12x - 14 + 3/4 = 12x - 14

Now, we will combine like terms:

12x - 14 + 3/4 = 12x - 14
12x - 56/4 + 3/4 = 12x - 56/4

Now, let's simplify both sides further:

12x - 53/4 = 12x - 53/4

Since both sides are the same, this equation does not have a unique solution.