We have that the decrease at the end of the year was of 7.5% of $8400. We can find this amount by multiplying 8400 by the decimal form of 7.5%:
we have that the decrease in dollars is $630.
Now, to find the amount that was in the account at the end of the year, we have to find the difference between 8400 and the decrease 630:
therefore, the year end amount is $7770