You can show subtraction for a problem like 32-15 by simply writing it out just like you did, horizontally: 32-15=. You can also show subtraction for 32-15 by stacking the numbers, with the larger number on top: 32
-15
Another way to show subtraction for 32-15 is by treating it as subtracting numbers with different signs: 32 is the same as +32-15. Or, you can switch the numbers around: -15+32, the answer will be the same, 17.
Hope that helped!