Let's start with m∠1. m∠1 <em>has </em>to be 90º because line segment AB is perpendicular with line segment AC, as it shows a right angle symbol on the angle beside m∠1. Now that we know that, it will be much easier to find m∠2 and m∠3 because m∠1, m∠2 and m∠3 are part of the triangle formed in the middle, and all angles in a triangle add up to 180º. 180-90 is 90, therefore, m∠2 +m∠3=90º so all three angles add up to 180º. You don't even have to find the specific angle measurements.
Hope this helps. I also attached a (rather poorly edited) image.
