Hello, Tuesday's Gone!

Your work is correct ... up to finding the length.

You found that the foot of the altitude is: .D:(24/17, -40/17) . Right!

Sorry, the book is right.The answer in my book says 6.55 units while I get approx. 9.12 units.

The distance from D:(24/17,-40/17) to A:(3,4) is:

. . . . . . . . _______________________

. . d . = . √(3 - 24/17)² + (4 + 40/17)² . = . 6.548461876 . ≈ . 6.55