If I read 30 pages the first day, 36 the 2nd day, 42 the third day and keep reading 6 more pages per day, how many days until I've read 270 pages?

Sounds like a setup problem to get you to use a modular formula, I can't remember what it looks like but something like n+1

Otherwise just make a normal x formula or x y formula that modulates the same way it does.
Something like
f(x)=30+x*6
f(0)=30
f(1)=36

once you have the formula just enter random values until you get around 270, like replacing x for 10 20 50. Then pick a bigger or smaller number until you get 270 or you might need to use decimals to find the more precise time(doubt it)
I hope that helped :)