2b
On the left side, use the measure of each angle.
On the right side, use 180 because the the sum of the measures of the angles of any triangle is always 180.
90 + 45 + <X = 180
135 + <X = 180
<X = 180 - 135
<X = 45
2c
90 + 56 + <H = 180
146 + <H = 180
<H = 180 - 146
<H = 34
3
A right triangle has 1 right angle measuring 90 degrees and two acute angles.
The sum of the measures of the three angles of a triangle is 180.
If you subtract 90 degrees (the right angle's measure) from the total of 180 degrees, 180 - 90 = 90, you get 90 degrees. That means that the sum of the measures of the two acute angles of a right triangle is always 90 degrees.