Too many people view their groundschool studies as if they were a race, with prizes being awarded for finishing in the minimum time. To win this race many students devote their entire efforts to simply memorising the answers to questions, without ever attempting to understand any of the subject matter. I'm not suggesting that you did so N1, but you probably know a lot of people who did.
Revising (some of) the ATPL theory subjects is certainly a good way of using the time while waiting for the employment situation to improve. To maximise the benefit gained, it should be viewed as a second chance to get to actually understand the material.
As Alex has said you do not need to draw anything to solve the question posed in this thread. But that does not mean nothing will be gained from doing so. They fact that you are asking where to draw the datum suggests that you will probably gain something from making a sketch.
A good starting point would be to ask what the information given in the question actually means.
If the C of G is located at 14.7% MAC, this means that it is 14.7% of the way back from the MAC leading edge to the MAC trailing edge
In this question the MAC is 82 inches from leading dege to trailing edge.
So the C of G is 14.7% of 82 inches aft of the leading edge.
As Alex has said, that is 14.7 x 82 / 100 = 12 inches aft of the MAC leading edge.
The question also states that the MAC leading edge is 103 inches aft of the datum.
So the total distance from the datum to the C of G is 103 + 12 = 115 inches.
If all of this is not obvious, it will help to draw a sketch.
As Tigermagicjohn has said, all of the distances given in the question are aft of datum, so we may as well draw the datum at the nose of the aircraft.
The MAC leading edge will be 103 inches aft of the datum.
And the C of G will be 12 inches aft of the MAC leading edge.
The sketch will show quite clearly that the C of G is 115 inches aft of the datum.