In a school there are w girls and x boys. y more girls and z more boys joined the school. How many girls are there in the school now?
There are w girls and x boys in the school.
y more girls join the school.
Now there are w + y girls in the school.
z more boys join the school.
Now there are w + y girls and x + z boys in the school.

The number of girls in the school now is w + y.