I'll do the first two problems to get you started.
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Problem 2
x = number of months
12x = number of pages after x months
12x+35 = total written after adding the initial 35 pages
Plug in x = 5 so we can find how much is written after 5 months.
12x+35 = 12*5+35 = 60 + 35 = 95
Answer: 95 pages
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Problem 3
x = number of days the book is late
0.15x = amount of extra fees, ignoring the $2.00
0.15x+2 = after adding on the initial $2 late fee
Set this equal to the amount Maria is charged so we can solve for x.
0.15x+2 = 3.20
0.15x = 3.20 - 2
0.15x = 1.20
x = 1.20/0.15
x = 8
Answer: Her book is 8 days late.