To find out how much ACA supply is left, you can subtract the amount of circulating supply from the total initial supply. Thus:
Total initial supply: 1 billion ACA
Circulating supply: 962.5 million ACA
So, to find out how much ACA supply is left, we subtract the total circulating supply from the initial total supply:
1 billion ACA - 962.5 million ACA = 37.5 million ACA
So, the remaining ACA supply is 37.5 million ACA.
