Answer is none of the above
Reason
The correct answer to the 3 numbers with a sum of 21 is 6,7,8 but those 3 numbers don’t make a product of 315
8,9,10 sum is 27 product is 720
2,3,4 sum is 9 product is 24
11,12,13 sum is 36 product is 1716
5,6,7 sum is 18 product is 210
So none of these will fit that criteria
You can find the sum of 3 numbers with equation
x+ x+1 + x+2 = 21
3x + 3 = 21
3x = 18
x = 6
x +1 = 7
x + 2 = 8