i don't know how you came up with 30 .000$.They gave the ending retained earning of 20000$, and want you to solve for beginning retained earning..
INCOME STATEMENT
Revenue: .............................2000
Expense: .............................(1000)
=Net Income:........................1000
Now the net income will go to the statement of retained earning
STATEMENT OF RETAINED EARNING
Beginning of Retained Earning ................. ???
Plus Net Income......................................1000
Less Dividends........................................(.....) in this case we have no dividend
Ending Retained Earning ..........................20.000
Now solve for "???" do a little math here (??? + 1000-0=20000)=>???=20.000-1000=19000$