To find out what percent 12 is of 40, you can use the following formula:
\[ \text{Percentage} = \left( \frac{\text{Part}}{\text{Whole}} \right) \times 100 \]
In this case, the part is 12 and the whole is 40:
\[ \text{Percentage} = \left( \frac{12}{40} \right) \times 100 \]
Now, calculate:
\[ \frac{12}{40} = 0.3 \]
Now multiply by 100:
\[ 0.3 \times 100 = 30 \]
So, 12 is 30% of 40.