How would i find the measure of number 6? i must show work or i'll get it wrong

So the interior angles of a triangle adds up to 180 degrees. And since it's an isosceles triangle (two sides are the same) the opposite angles (angle EFD is opposite to length ED) are equal.
So:
180=2x+40
120=2x
60=x

The two lines show that the other two angles are the same (meaning they have the same angle number) a triangle has 180 degrees. Subtract 40 from that and you will get 140. Divide that by 2 for the other two sides and you will get that the angles are both 70 degrees