A, C and D are all using estimation to check the result.
A is rounding to the nearest multiple of 100.
267 --> 300
154 --> 200
C is rounding to the nearest multiple of 50.
267 --> 300
154 --> 150
D is rounding to the nearest multiple of 10.
267 --> 270
154 --> 150
Those each give you an estimation of the final answer to see if 113 is a reasonable answer.
Method B is just switching the values around to check the subtraction using addition. That's a valid way to double check the result, but is NOT estimation.
If you are only expected to give *one* answer, then method D is the best way to check using estimation because it does the least amount of rounding.
Answer:
D. 270 - 150 = 120
