So let's say that the second angle is x.
Then we can say that the third angle is
.
So then we have three angles:
1) 66°
2) x°
3) (
)°
So then we can add these together and solve for x by setting it equal to the total degrees left in the triangle after subtracting the known angle:





So now we know that the measure of the second angle is 38°. So then we can use this value to solve for the third angle:

So the values of the angles are:
1) 66°
2) 38°
3) 76°
There are several ways to confirm that the two expressions are equal. One method is to simply factor the first expression and see it you get a result equal to the second expression. An easier method is to set a value for x and substitute it to the two expressions. If the resulting value is that same, this means that the two expressions are equal.
8.545 rounded to the nearest tenth is 8.5. I hope this helps.