I need to solve for angle A, a quick response would be appreciated!

Answer:
x = 21
Explanation:
The two remaining angles must add to 90 degrees since a triangle adds to 180
3x+6 +x = 90
4x+6 =90
4x = 90-6
4x = 84
Divide by 4
4x/4 = 84/4
x = 21