D. Grant did not regroup the 4 tens when he subtracted 7.
Step-by-step explanation:
In the process of subtraction, regrouping is important so that each digit in the given numbers are placed appropriately before the required arithmetic operation is performed.
The correct step to Grant's solution are:
360 - 100 = 260
260 - 20 = 240
240 - 7 = 233
Grant's final answer ought to have been 233.
Going through his solution, he made a mistake while subtracting 7 from 240. He failed to regroup the 4 tens when he subtracted 7 from 240. Thus the essence of his wrong answer.
