To find out what percentage 42 is of 75, you can use the formula:
\[ \text{Percentage} = \left( \frac{\text{Part}}{\text{Whole}} \right) \times 100 \]
So, in this case:
\[ \text{Percentage} = \left( \frac{42}{75} \right) \times 100 \]
Calculate this expression to find the answer.