equity as of the beginning of the year= $ 51400

Working notes for the above answer

We have been provided with the information as follow

equity  at the end of the current year.
$57,100

investments by owners in exchange for stock
8400

net loss
-2700

Now we will calculate equity as of the beginning of the year

equity  at the end of the current year.
$57,100

Less:
 

investments by owners in exchange for stock
8400

 
$48,700

Add:
 

net loss
2700

 
$51400