I'm stuck : (
ps it's worth 100 points!

You just gotta plug in those numbers, so:

A=a+b/2*h

40=(x+3)+x /2 * 2x

The area of a trapezoid is (b1+b2)/2 times height
So if we plug in our values it will be 
(x+x+3)/2 times 2x
Simplify
(2x+3)2 times 2x
(4x^2+6x)/2
And finally we simplify down to 2x^2+3x
Now we know that this equals 40, so...
2x^2+3x=40
Put the 40 on the other side
2x^2+3x-40=0
Now find the positive zero which is 3.785
Add 3 because we are looking for the long base and get 6.785
round it to nearest tenth and get 6.8
Do you get it?

The area is about 10 in.

Step-by-step explanation:

3 x 3 = 9 rounded to 10