34.

Let n be the number of hours he spent on the 1st day.

n + (n+2) + (n+4) + (n+6) = 24
4n + 12 = 24
4n = 12
n = 3

So he spent n+6 = 9 hours on the last day.

33.

Let S be the sum total of bookmarks Peter has.
Let n be the number of cousins Peter has.

S – 7n = 3
=> (1) S = 8 + 7n

S – 9n = -5
=> (2) S = -5 + 9n

So placing (1) and (2) together,
8 + 7n = -5 + 8n
n = 13

Substituting into (1), S = 8 + 7(13) = 99 #

32. Let n be the number of months.

376 + n*90 >= 1299
90n >= 1299 – 376 = 923
n >= 923/90 = 10.26

So n = 11 #