Hey there!
To find percent error, we find the difference between the prediction and the actual value. We take that difference, divide it by the prediction, and multiply it by 100.
So let's find the difference.
42 - 30 = 12
Divide the difference, which is 12, by 30.
12 ÷ 30 = 0.4
Multiply this by 100 to get the percent.
0.4 x 100 = 40
The percent error is 40%.
Hope this helps!