Answer:
13
Step-by-step explanation:
as I understand double fact i'ts like
a+a=2a
something like that
you could use two ways
1) first way
that 6=7-1
so you get
7+7-1
=14-1
=13
and you get the answer
2) second way
that 7=6+1
so you get
6+1+6
=6+6+1
=12+1
=13
and you get the same answer
