Okay so first I just go to the wording of the first part, reading it again as something like "85 is 34% of what number?" Then I translate it by putting an = for the "is", an x (times) for the "of", and a variable, w for "what number". Because it's a percent, we get rid of the % sign by writing 34/100, or .34 . Then we just have:
85=.34 x a
Divide off the .34
a=250
Now for the second part. 250 is the total number of pages, so subtract 85 to get the number of pages she hasn't read.
250-85=165
So she has more than 125 pages left.