Ok, so here's how you do it.Since you have those two 21s, you know those sides are equal, which means that you're gonna make an equation 38+2x=180 because all angles in a triangle have to equal 180 and whatever that x equal is also what that other missing angle is I think because of those two sides being equal and then you're going to solve that equation for x, so you wanna get x by itself. You subtract that 38 from the sides it's on and do the same to the other side, so 180-38, which equals 142. So now you have 2x=142, you have to get x by itself, so to do that you divide by 2 on both sides, so 142/2=71, so x=71.Hope that helps.