Answer
$A: 0,0 \\ B: 2a,2b \\ C: 4a,0$
Work Step by Step
An ideally placed triangle, which we will call triangle ABC, should have point A placed at the origin and side AC be on the x-axis. Calling the length of AC "4a" and the height "2b," we obtain:
$A: 0,0 \\ B: 2a,2b \\ C: 4a,0$
Note, we double all of the numbers from last problem, for the book wants midpoints, which are equal to the length of half of a side.