% error = [tex]\frac{|accepted - measured|}{accepted} *100[/tex]
now, we plug in your data:
[tex]\frac{|accepted - measured|}{accepted}*100 \\ \frac {|30-24|}{30}*100 \\ \frac {6}{30}*100 \\ \frac {6}{30}*100 = 20[/tex]
therefore, Kayla's percent error is 20%