Hello. Did you try anything? I learned the proportion method, in arithmetic class. (I don't know what class you're taking.)
\(\displaystyle \dfrac{\text{Part}}{\text{Whole}} = \dfrac{\text{Percent}}{100}\)
Your exercise gave you the part and percent. You need to find the whole. The whole refers to the whole group of factory workers. Part of that whole is a smaller group (550 workers).
The part compares to the whole the same way the percent compares to 100. Write the proportion:
\(\displaystyle \dfrac{550}{\text{Whole}} = \dfrac{55}{100}\)
To find the missing number, we can use the pattern that says, "Multiply on the diagonal and divide by the number not used."
550 × 100 ÷ 55 = ?
?