A number is decreased by 9. If the obtained number is multiplied by 7, it gives 21. Find the number.

Options

A. 15
B. 14
C. 13
D. 12

Answer

To solve the problem step by step, we will follow the instructions given in the question.

### Step 1: Define the variable
Let the unknown number be represented by \( x \).

### Step 2: Set up the equation based on the problem statement
According to the problem, the number is decreased by 9. This can be expressed as:
\[ x - 9 \]

### Step 3: Multiply the result by 7
The problem states that this result (the number decreased by 9) is multiplied by 7, which gives 21. We can write this as:
\[ 7(x - 9) = 21 \]

### Step 4: Solve the equation
Now, we will solve the equation for \( x \).

1. Divide both sides of the equation by 7 to isolate \( x - 9 \):
\[ x - 9 = \frac{21}{7} \]
Simplifying the right side:
\[ x - 9 = 3 \]

2. Now, add 9 to both sides to solve for \( x \):
\[ x = 3 + 9 \]
Simplifying this gives:
\[ x = 12 \]

### Final Answer
The number is \( 12 \).

---