You put $10,000 in an account earning 5%. After 3 years, you make another deposit into the

Question:

You put $10,000 in an account earning 5%. After 3 years, you make another deposit into the same account. Four years later (that is, 7 years after your original $10,000 deposit), the account balance is $20,000. What was the amount of the deposit at the end of year 3?