Query re Residual Calculation

Hi all!

I have obtained the following model:

y = 62.3651 + 0.662697x

The y variable represents the cholesterol level after 4 days whilst the x variable represents the cholesterol level after 2 days.

The blood cholesterol level 2 days after having a heart attack was 142 mg/dl. And four days after having a heart attack it was 116 mg/dl. I've been asked to use the above model in order to calculate the residual for this patient.

Below are my workings:

In order to bring out an estimate for the blood cholesterol level after 4 days I did the following:

62.3651 + 0.662697(142) = 156.47

Now the cholesterol level after 4 days was 116 so the residual is 156.47 - 116 = 40.47 mg/dl

Is my reasoning and working correct?

Thanks