Answer:
a.$900
Step-by-step explanation:
The required reserve is the amount of reserve required by the Central bank for banks to keep as reserves.
If the reserve ratio is 10% and $1000 is deposited, the required reserve is $100.
$1000 - $100 = $900 would be available to banks to give out as loans. Thus , money supply increases by $900.
I hope my answer helps you.