Need help finding one of the bases

I have a trapezoid with a top base (b_{1}) of 10 and a height of 5.

Considering the area, find b_{2 }Do I need to find the area first? If so, can someone explain how I go about that. You don't need to give me the answer, but I'm not sure where to start.

Thanks!

Re: Need help finding one of the bases

The area of a trapezoid is the average of the two unequal bases times the height:

So if you know the values for A, b1 and h, you can solve for b2.

Re: Need help finding one of the bases

right, but I only have h=5 and b1=10

Re: Need help finding one of the bases

If you don't know the area you can't determine b2, and if you don't know b2 you can't find the area. There must be something else they've told you in the problem - is there a figure?