I'm really confused about question d and need does anyone know what it is?

Boys:girls = 2:3

This is the same as saying boys make up  of the class. (2 parts out of a total 5 parts - because 2 + 3 = 5 - are boys.)

To make it a percentage, you convert the fraction to decimal and then multiply by 100.

So:

= 0.4
0.4 × 100 = 40%.

Bis the correct answer