Explanation:
7 + 7 = 14
find the sum of 6 + 7
7 + 7 = 14 is one of the closest double to 6+7.
W.K.T(we know that)...
7 is 1 more than 6 this means ;
7 + 7 will be one more than 6 + 7
7 + 7 = 14 finding 1 Less
6 + 7 = 13
here is the answer hope It helped you