Hello, Wary,
Use the conversion units given. Since 1 inch = 2.54 cm, we can write it either as (1 inch/2.54 cm) or 2.54 cm/1 inch. Both are equivalent to "1," so they can be multiplied times anything to make a conversion. Ibn the case, we want to go from inches to cm, so let's pick the most convenient form of the conversion, 2.54 cm/1 inch. When we multiply that times 6 inches, the inches cancel and we are left with 6 x 2.54 cm as the answer. I can see which is the correct choice without even using a calculator.
I hope this helps,
Bob
