Answer:

Explanation:
The gist of modular arithmetic in a nutshell: the numbers
and
are considered to be congruent by their modulus
if
is a divisor of their difference.
In mathematics:

Exemplifying this:
because
,
.
Let us have following equivalences:
and
, then:
and
by definition.
Properties:
1.
.
2.
.
3.
.
4. What if we have
twice? If we abide by property 3, we can come to the conclusion that
. It is fair enough that there is room for the equivalence
.
.
We used property 4.
Keep in mind that any remainder cannot be a negative number.
Therefore, the remainder equals
.