Simplify the following expression: -4 of [2 ÷ 84 ÷ 7 - 1]

"of" means multiplication. Perform divisions from left to right.

The value of the expression is $\boxed{\frac{586}{147}}$.

Let the tens digit be $t$ and the units digit be $u$.
The number can be represented as $10t + u$.

Condition 1: The product of the digits is 20.

Condition 2: When the digits are reversed, the new number is greater than the original number by 9.
The reversed number is $10u + t$.

Subtract $u$ and $10t$ from both sides:

Divide by 9:

From (2), we can express $u$ in terms of $t$:

Rearrange into a quadratic equation:

Factor the quadratic equation:

Possible values for $t$ are $t = -5$ or $t = 4$.
Since $t$ is a digit of a positive two-digit number, it must be a positive integer between 1 and 9.
Therefore, $t = 4$.

The number is $10t + u = 10(4) + 5 = 45$.

Product of digits: $4 \times 5 = 20$ (Correct).
Reversed number: 54.
Difference: $54 - 45 = 9$ (Correct).

The number is $\boxed{45}$.

The solution for $x$ is $\boxed{\frac{3}{2}}$.