we know that
The residual value is the observed value minus the predicted value.
RESIDUAL VALUE=[OBSERVED VALUE-PREDICTED VALUE]
where
Predicted value.--> the predicted value given the current regression equation
Observed value. --> The observed value for the dependent variable.
in this problem
predicted value for x=3 approximate y=3.6
observed value is for x=3 y=5
so
RESIDUAL VALUE=[5-3.6]------> 1.4
the answer is
the best estimate of the residual is 1.5