Answer:
380 + 6 + 14
Step-by-step 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
20 most likely multiply it and see
Use the Pythagorean Theorem.

What do you think the answer is?
True. because a negative times a positive will equal out to a negative