two angles are called complementary when the sum of them is 90 degrees. so we have two angles the
angle a and the angle b , they are complementary angles, that is a+b=90 we know that a/b = 2/3 as well.
from the first equation we have a = 90-b putting this value to the setcond one we have 90-b/b = 2/3
or 3(90-b) = 2b -->>> 270-3b = 2b -->>> 270=3b+2b or 270=5b and b=270/5 b=54 so a=90-54
a=36