The reason it's important to use an absolute reference is so that the formula can be properly filled down in Question 6.
You're right that using $E$3 or E$3 would both be correct answers in this case, since the formula only needs to be filled down and is never filled across. However, since there is no possibility that you would ever want Excel to adjust references to cell E3 it's still better to use $E$3 as it eliminates any possibility of a mistake.
Another advantage of the $E$3 approach is that you can apply it with a single keystroke by simply pressing <F4> after selecting the cell while building your formula.
You can find a complete explanation of absolute and relative cell references in the video lesson: Essential Skills Lesson 3-12 Understand absolute and relative cell references.
I hope this is the answer you were looking for, but please feel free to reply if you have any more questions about this.
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