The absolute error is 4 cu. in. and the relative error is 10%.
To find the absolute error, subtract the actual value from the estimate:
36 - 40 = -4
With absolute error, we ignore negative signs, so the absolute error is 4 cu. in.
To find the relative/percent error, divide the absolute error by the actual value:
4/40 = 0.1
Converting this to a percent, 0.1(100) = 10%