This is the computer regression output given.
Breadth (mm) is the explanatory (x) variable in this situation and mass (g) is the response (y) variable.
We need the slope and the y-intercept to write the equation of the regression line in the form \widehat{y}=a+bx
The constant coefficient -266.53 is the y-intercept and the breadth coefficient 6.1376 is the slope
So, the equation of the least-squares line is \widehat{y} = 6.14 x -266.53.
Now, plug in x = 35 mm, in this to get \widehat{y} = 6.14 \cdot 35 - 266.53 = -51.63 g.
The residual is the difference between the observed value y and the predicted value \widehat{y}.
Residual = 39 g - 51.63 g = -12.63 g.
So, the residual of a 39 g falcon chick who hatches from an egg with a breadth of 35 mm is -12.63 grams.