You can read posting Sarin and his coin bank on the story of coin bank.
Lower primary school mathematics question LPQ11
Sarin collected a total of 401 Singapore and American coins. There were 109 fewer Singapore coins than American coins. How many American coins did Sarin collect?
Sarin collected (401- 109) ÷ 2 = 146 of Singapore coins.
Hence, Sarin collected 146 + 109 = 255 of American coins