Answer: Grant did not regroup the 4 tens when he subtracted 7.
Everything else he did was correct! When got down to the bottom he made a mistake.
Because there was a zero, grant should have token away from the 4 in which it would become a 3 and given to the 0 so it would become a 1. Due to the fact that he did not do this he got it wrong.
Hope this helps:)