3/5 of the class are class are girls, hence:
1 - 3/5 = 2/5 of the class are boys

1/3 of the girls wear glasses:
so the fractiom of the class that are girls AND wear glasses is 1/3 x 3/5 = 1/5

1/4 of the boys wear glasses:
so fraction of class that are boys AND wear glasses is 1/4 x 2/5 = 1/10

So total fraction of class that wear glasses:
1/10 + 1/5 = 1/10 + 2/10 = 3/10

Hence 3/10 of the class wear glasses