Write a query in XQuery on the XML representation as shown below to find the total balance, across all accounts, at each branch. 

<bank>

<account>

<account-number> A-101 </account-number>

<branch-name> Downtown </branch-name>

<balance> 500 </balance>

</account>

<account>

<account-number> A-102 </account-number>

<branch-name> Perryridge </branch-name>

<balance> 400 </balance>

</account>

<account>

<account-number> A-201 </account-number>

<branch-name> Brighton </branch-name>

<balance> 900 </balance>

</account>

<customer>

<customer-name> Johnson </customer-name>

<customer-street> Alma </customer-street>

<customer-city> Palo Alto </customer-city>

</customer>

<customer>

<customer-name> Hayes </customer-name>

<customer-street> Main </customer-street>

<customer-city> Harrison </customer-city>

</customer>

<depositor>

<account-number> A-101 </account-number>

<customer-name> Johnson </customer-name>

</depositor>

<depositor>

<account-number> A-201 </account-number>

<customer-name> Johnson </customer-name>

</depositor>

<depositor>

<account-number> A-102 </account-number>

<customer-name> Hayes </customer-name>

</depositor>

</bank>