Solve: `x-40%` of `x=12`.

Answer

To solve the equation \( x - 40\% \text{ of } x = 12 \), we will follow these steps:

### Step 1: Write the equation
The equation can be expressed as:
\[ x - 0.4x = 12 \]

### Step 2: Combine like terms
Combine \( x \) and \( -0.4x \):
\[ (1 - 0.4)x = 12 \]
This simplifies to:
\[ 0.6x = 12 \]

### Step 3: Isolate \( x \)
To isolate \( x \), divide both sides of the equation by 0.6:
\[ x = \frac{12}{0.6} \]

### Step 4: Simplify the division
To simplify \( \frac{12}{0.6} \), we can multiply the numerator and the denominator by 10 to eliminate the decimal:
\[ x = \frac{12 \times 10}{0.6 \times 10} = \frac{120}{6} \]

### Step 5: Perform the division
Now, divide 120 by 6:
\[ x = 20 \]

### Final Answer
Thus, the value of \( x \) is:
\[ \boxed{20} \]

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