Answer:
380 + 6 + 14
Explanation:
The sum of 386 and 14 is 386 + 14 = 400.
To find which stategy he used, we find the results of each sum, and it has to be 400.
380 + 6 + 14
380 + 6 + 14 = 386 + 14 = 400
So this is the strategy that he could have used.
380 + 14 + 14
380 + 14 + 14 = 394 + 14 = 408
Result different of 400, which means that this was not the strategy
386 + 10 + 4 + 14
386 + 10 + 4 + 14 = 386 + 14 + 14 = 408
Result different of 400, which means that this was not the strategy
386 + 14 + 80 + 6
386 + 14 + 80 + 6 = 400 + 86 = 486
Result different of 400, which means that this was not the strategy