Since you did not state the center of dilation, I will
assume you meant the center of dilation to be the origin.

A(8,-24), B(8,-8) and C(16,-8)



In that case, we multiply all the coordinates of

A(8,-24), B(8,-8) and C(16,-8)

by 1/4, and get 

A'(2,-6), B'(2,-2) and C'(4,-2)

We draw the dilated triangle A'B'C' in red also, and
green lines from the origin through the coordinates:



I know you just wanted A' but you need to understand what's
going on, not just a cookbook way to get an answer.  It's
very hard to learn math the cookbook way without understanding
what's going on.  Understanding is what makes math easy.

Edwin