First question:
Right triangle means one angle is 90 degrees.
All angles added is 180 degrees.
Therefore, the last angle is 180 - 90 -35 = 90-35 = 55 degrees
Second:
Isosceles triangle has two equal base angles. Call each one x.
So 58 + 2x = 180
2x = 122
x = 61 degrees = measure of base angle