This scatter plot and line of best fit show the relationship between the height and the mass of 15 different dog breeds. The circled point in the scatter plot corresponds to the Afghan Hound. What conclusion can be drawn about the predicted mass and the actual mass of the Afghan Hound?

The mass of the Afghan Hound is exactly what is predicted by the line of best fit.

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4