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!
to do subtraction
to teach subtraction
to learn subtraction
Of course I can do subtraction!
A subtraction, for example, is "subtracting two from six equals four."
Although it is a elementary school third grade level subtraction problem, I still can't figure out the answer.