To convert 31 inches to cm, there are a few steps to follow:

1. First, we need to know the conversion factor between inches and cm. This conversion factor is 2.54 cm per inch.

2. Then, we will set up a proportion using the given value of 31 inches and the conversion factor. The proportion will look like this: 31 inches = x cm / 1 inch = 2.54 cm.

3. To solve for x, we need to cross-multiply the equation, which gives us 31 inches times 2.54 cm = x cm. This simplifies to 78.74 cm = x cm.

4. Finally, we can state the answer as 31 inches is equal to 78.74 cm.

So, the final conversion of 31 inches to cm is 78.74 cm.

Another way to do this calculation is by using the formula: cm = inches x 2.54.

Therefore, cm = 31 inches x 2.54 = 78.74 cm.

As you can see, both methods provide the same result. It is important to remember to always use the correct conversion factor and set up the proportion correctly when converting units of length. Now, you can confidently help others convert between inches and cm.