Of course I can do subtraction!
Subtraction class is so long that I can't stop yawning.
What year of grade school will we learn subtraction?
Remember how 引く means "to subtract?" Add calculate to that and you'll have subtraction! It's the type of calculation you're doing when you subtract.
This is the kun'yomi reading for 引 and the on'yomi for 算. And the さん reading is rendaku'd into ざん. This is the same for all the math-ish words (addition, subtraction, multiplication, and division), so try to remember that, because you'll see it again!