That's an interesting question! I don't have aphantasia, and can visualize things pretty vividly - but I also resorted to "verbal memory" to do that calculation

That's an interesting question! I don't have aphantasia, and can visualize things pretty vividly - but I also resorted to "verbal memory" to do that calculation. I foiled it like the other comment says (maybe somewhat of a visualization, since I "visualized" it as 40x60 + 40x8 + ...), and I remember the running sum by "saying" it to myself inside my head. I performed each multiplication (grade-school multiplication memory lookup table, not actually doing the visual algorithm) and added the right number of 10's place zeros, then added it to the running sum. For this addition step actually, I do visualize as stacking the two numbers and carrying if needed. Then I "say" the result to myself and remember it for the next multiplication. I will say that my first reaction to seeing "calculate 47x68 real quick" was reluctance and it was not an easy task to do mentally, but it was mechanically straightforward.