The answer would be 1.88062% for everybody in your group.
%error is calculated by doing |(value observed - expected value) /expected value. Then, after you figure that out, you multiply the equation by 100
In this case, your value observed is 12m and the expected value is 12.23, so it would be |12 - 12.23| = |-0.23| The straight lines make the answer, no matter what, positive, so it would be 0.23. Then, we do 0.23 / 12.23 = 0.0188062
0.0188062 x 100 = 1.88062%