Can someone pls pm me your child index number for me to waive my gal registration fee. Thank you.

Pls help me on this question.


In a class of 42 pupils, each boy received 3 stickers and each girl received 4 stickers from their teacher. Altogether the teacher gave out 154 stickers. How many girls were there in this class?

The answer is :
42 x 4 = 168
168-42 = 126
154-126 = 28

But I do not understand why 168-42 ?