What does this math question mean

Question

There are 30 students in a class there are 4 more boys than girls what is the equation

the answer in the answer book was 2x+4=30 what does this mean?

Answer 1

Let x = number of girls in the class

Then, x + 4 = number of boys in the class

So, x + (x + 4) = 30

That is, 2x + 4 = 30