How do you subtract $ 9-12 $ ?

Hint: We first explain the concept and use of the number line. We follow the conditions for addition and subtractions. We take one term at a time to find the additional value.

Complete step by step solution:
In math, a number line can be defined as a straight line with numbers placed at equal intervals or segments along its length. A number line can be extended infinitely in any direction and is usually represented horizontally.
So, to represent the given addition $ 9-12 $ in the number line, we need to follow some rules. The more we go to the right of the number line the greater the number becomes and the more we go to the left of the number line the lesser the number becomes. So, to add a positive number we need to go right and to subtract a positive number we need to go left.

Therefore, we first went 9 steps towards the right and then went left 12 steps from there to reach $ -3 $ .
Algebraically we can also verify that $ 9-12=-3 $ .
So, the correct answer is “-3”.

Note: The number line is a pictorial representation of numbers on a straight line. It’s a reference for comparing and ordering numbers. It can be used to represent any real number that includes every whole number and natural number.