Hi!
So the angles make a right angle which is also known as a complementary angle.
What you want to do is set both terms equal to 90
11x + 4x = 90
15x = 90
divide by 15
x = 6
now multiply 6 by 4 because you want to know whata angle 3 is
6*4 = 24
24 degrees is your answer!
Hope this helps!