Since $900 is the discounted price, we need to find out the original price. The discount given was 10% hence 90% of the price is $900.
90% - - > $900
100% - - > $900/9 * 10
100% - - > $1000
(If you do not understand, 90% can be seen as 90/100 = 9/10. Hence 9 units is $900, 10 units is $1000)
Discount given is $1000 - $900 = $100

For his membership he was given another 10% discount on the discounted price of $900.
100% - - > $900
10% - - > $900/10
10% - - > $90
So the total discount he received is $100 + $90 = $190
Option 1 is the answer.