Divide: 6 ÷ 1 2 = 12 To verify the answer with a model, you could show circles. Each circle would be divided into equal parts. parts would be shaded.

12.5 units

Explanation:
We are given that:
ΔABC ~ ΔDEC
This means that the similarity proportion can be set up as follows:
AB/DE = BC/EC / AC/DC

We have:
CD = 5 units
BC = 6 + 4 = 10 units
EC = 4 units

This means that:
BC/EC = AC/DC
10/4 = AC / 5

Therefore,
AC = (5*10) / (4) = 12.5 units

Hope this helps :)