Question 16275
As you probably know, the base angles in an isosceles triangle are equal.  Let's call one of these base angles x.
And you are also most likely aware that the sum of the interior angles of any plane triangle is 180 degrees. From the problem description, we can write: (2x - 40) is the vertex angle.
Putting it all together then, we can wite:

{{{2x + (2x-40) = 180}}} Simplify and solve for x.
{{{4x - 40 = 180}}} Add 40 to both sides.
{{{4x = 220}}} Divide both sides by 4.
{{{x = 55}}}

Each base angle is 55 degrees.

The vertex angle is: 2(55) - 40 = 110 - 40 = 70 degrees.

Check: 55 + 55 + 70 = 180