Since the question is asking how many pencils the teacher will have to give out, we can automatically ignore the 46 erasers from the problem because it is not relevant. The information was most likely put there to confuse you.
Each student is getting 28 pencils, so if we multiply the number of students by 28 pencils, we will find how many pencils the teacher will need to give out.
There are 42 children in the classroom, so multiply 42 by 28.
42 * 28 = 1,176
The teacher will have to give out <u>1,176 pencils</u> to her 42 children in the classroom.
So it is really easy to solve firstly we can see how much does the first 10 boxes make which makes around 75$ obviously. Secondly 55$ for the next 10 boxes.
So for now we can simply calculate that we have spent around 130$ which means 20 boxes. The remaining money left is 18$ so we can buy 18/4.5 = 4 only 4 boxes with that money. Hence a total of 24 boxes.