First, you have to divide the area by the height (or 144 by 8) which would give us 18. Now, multiply that by 2 to get 36 and then subtract the length of the first base (or 12) to get 24.
To find the average size of the bases, divide the area by 8. 144/8 = 18 Next, subtract 12 from 18 then add that number to 18 to find the other base's length. 18 - 12 = 6 18 + 6 = 24 The length of the base is 24.