What is 8 times 9 in 12-hour clock arithmetic? What is $8\times 9$ in $12$ hour arithmetic?
Will it be $0$, or will it be $6$?
$8*9 = 72$ and $72/12 = 6$
So is the answer $0$ or $6$?

Remember,
$$a\equiv b\bmod n\;\iff \;n\text{ goes into }a-b,$$
or in other words,
$$a\equiv b\bmod n\;\iff \;\text{dividing }a-b\text{ by }n\text{ leaves no remainder}.$$
Using this definition, which statement is true:
$$72\equiv 0\bmod 12$$
or
$$\;\;\;72\equiv 6\bmod 12 \;?$$
