Jen wrote 10 times as many pages of a school report as tom. they wrote 396 pages altogether. how many pages did each student write?

Let's call the number of pages that Jen wrote "j".

then tom (t) wrote:

What we know:

j=10t

this means:

t=0.1 j
and j+t=396

for this it's practical to substitute j with 10 t:

10t+t=396

11t=396

we divide both sides by 11:
t=36

so tom wrote 36 pages, and Jen wrote ten times as much, or 360 pages (that's a lot!)

The shelves will hold 270 books in total