To find out her income in the first week, add $125 to 10% of 800.
125+(800*.1)=205
In the first week, she earned $205.
For the second week, you're trying to find out how much in books she sold. To find the value of the books she sold, subtract 125 from 225 and divide by 10%.
225-125=100
100/.1=1000
She sold $1000 worth of books in the second week