An easy way to think of this when you solve this, is to remember that all the angles in a triangle add up to 180 degrees. Therefore, the equation would be
(3x + 10) + (2x + 10) + 45 = 180. By the way, since the angles D and B are across from each other they are congruent. Now, let’s start solving it:
(3x + 10) + (2x + 10) + 45 = 180
(5x + 20) + 45 = 180
5x + 65 = 180
5x = 115
x = 23