Answer:
Liam has 4 books. First book is 420 pages, The second book has 70 more pages than the third book while the third and fourth is 150 pages each.
150 + 70 = the second book has 220 pages
420 + 150 + 150 + 220 = 940 pages
And if its asking for the "mean" then take 940 / 4 and you will get 235