A triangle has to equal 180 degrees in total. Because you know it is a right triangle and b is the right angle you make angle a plus c equal 90. You add together 8x and 9x to get 17x and add the 2 and 3 to get 5. You have to solve for x so you subtract 5 from both sides to get 17x = 85. To get x alone you divide both sides by 17 giving you x=5. Now that you have x you plug it into to the equation for angle a. This gives you 8(5)+2 which equals 42.
