To find a you divide 90 by 2 which equals 45. So a=45
A circle has 360 degrees. So you add 90 and 110 together and get 200 degrees. So to find the rest you subtract 200 from 360.
360-200=160 degrees.
To find b we divide 160 by 2 and that equals 80. So b=80.
a+b=45+80=125.
The answer is B