15 x 25 = 375
15 x 50 = 750
375 + 750 = 1,125
She has 1,125 books.
Answer:
The sum of the first 880 terms in the sequence is 2,273,920.
Step-by-step explanation:
Arithmetic sequence:
The difference between consecutive terms is always the same, called common difference, and the nth term is given by:

In which d is the common difference.
Sum of the first n terms:
The sum of the first n terms of an arithmetic sequence is given by:

ai = ai-1 + 6
This means that 
In this question:
Sum of the first 800 terms, so 
First term is -53, so 
The 880th term is:

Sum

The sum of the first 880 terms in the sequence is 2,273,920.
We have to make an equation: a number increased by 10 is 114.
An equation is:
x + 10 = 114
x = 114 - 10
x = 104.