The percent error is calculated by the formula Absolute Value of (Error - Actual / Actual then times 100).
In this case the Error value was 76, and the Actual was 80.
So, set up the expression
I(76 - 80)/80 x 100I
I-4/80 x 100I
I-400/80I
I-5I
5
The percent error was 5 percent, since that was how much her estimation differed from the actual amount.
5 percent