CLASS-1
SUBTRACTION THROUGH COUNT-BACK

SUBTRACTION THROUGH COUNT BACKWARDS 

PROBLEM.1) - Subtract 9 from 30 through Number Line.

SOLUTION -

Start from 30, count 9 space backward. You will reach 21.

PROBLEM.2)- Subtract 12 from 25.

SOLUTION -

Start from 25, count 12 space backward. You will reach 13.

So, in single step -