Subtracting 1 Digit Numbers from 2 Digit Numbers

 1 EASY What is $$13-0$$?

 2 EASY What is $$11-2$$?

 3 EASY What is $$21-4$$?

 4 EASY What is $$17-5$$?

 5 MEDIUM What is $$14-9$$?

 6 MEDIUM What is $$99-9$$?

 7 MEDIUM What is $$11-7$$?

 8 MEDIUM What is $$21-3$$?

 9 HARD What is $$22-8$$?

 10 HARD What is $$67-9$$?