Question about determining digits of a number

[GeoMike]

The question is:
If $$\sqrt{ABADEC} = BEB$$ what is the value of the digit "D"?

I'm completely lost as to how to start on this one. I tried expanding the numbers as powers of ten:
BEB = B*10² + E*10¹ + B*10⁰
= B(10² + 1) + 10E
= 101B + 10E
...but I couldn't really do anything with it after that.

I don't want an answer, just a hint on how to proceed.

Thanks!
-GM-

 

[shmoe]

BEB = B*10² + E*10¹ + B*10⁰

Try taking this expression and squaring it.