Explanation:

- The number of boys in the class is 45% of the total number of students.

- The number of girls in the class is given as 33.

- Let the total number of students be $x$.

- Therefore, the number of boys is $0.45x$.

- Since the rest of the students are girls, number of girls = Total students - Boys.

- Substitute the numbers: $x-0.45x=33$.

- Simplify: $0.55x=33$.

- Solve for $x$: $x=\frac{33}{0.55}=60$.

- Thus, the number of boys is $0.45\times 60=27$.

- Option 1: 27 is correct.