Draw a number line starting at 0 and mark off interval divisions 1 to 10 to the right of 0. You don’t have to draw anything accurately as long as you mark clearly and make sure all numbers are in order.
Starting at the marked division 9 move 4 divisions backwards towards 0. You should end at division 5. So 9-4=5. Remember on a number line that plus means go right (forwards) and minus means go left (backwards).