Answer: First option
The numbers are 11, 12, 13
11+12+13 = 36
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Explanation:
Here's one way to solve for n
n+(n+1)+(n+2) = 36
3n+3 = 36
3n = 36-3
3n = 33
n = 33/3
n = 11
That leads to n+1 = 11+1 = 12 and n+2 = 11+2 = 13
So the three numbers are 11,12,13
11+12+13 = 23+13 = 36 which confirms the answer
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For the second option, it's not clear how the student got n = 15. If I had to guess, they probably divided both sides by 3, then added 3 to both sides.
As a quick check, 15+16+17 = 31+17 = 48 which doesn't match up with the 36.
Or you could note that the units digits add to 5+6+7 = 11+7 = 18. That 8 doesn't match with the 6 in 36. So this is an even quicker way to rule out the second option.
