Thank you. Then could you please let me know what would be the difference between the balances of the two accounts?
SELECT T3.balance - T2.balance FROM accounts AS T1 JOIN checking AS T2 ON T1.custid   =   T2.custid JOIN savings AS T3 ON T1.custid   =   T3.custid WHERE T3.balance  >   ( SELECT avg ( balance )  FROM savings ) 
difference between the balances of two accounts refers to T3.balance - T2.balance; two accounts refers to checking and savings accounts; condition for one account balance being greater than the average balance of savings accounts refers to T3.balance > (SELECT AVG(balance) FROM savings);