See the attachment. I'm subtracting the 2 coefficient radical from the 3 coefficient radical on the left. then cubing each side of the equation. I'm trying other things but I can't get 125/4
This, my friend, is where confidence comes in.
If you are SURE you proceeded correctly, your predecessor must have been incorrect.
If you are not SURE, keep at it until you ARE SURE.
As you have stated the problem, you are exactly correct. The question that remains is, "Did you state the correct problem?"