Since there are already two angles given for the triangle, we can measure the last angle using this formula:
90 + 55 + a = 180
Now solve for "a".
90 + 55 + a = 180
145 + a = 180
a = 180 - 145
a = 35°
For b.
From the picture above, the two triangle's tip are touching and having to form <em>vertical angles. </em>This means that the angles are congruent to each other.
Now that we have two angles in the second triangle(35 and 120), we can use the same formula: