We are give the fact that
[tex]m < a + m < b = 110 \: so \\ \frac{1}{2}m < a + \frac{1}{2}m < b = 55[/tex]
By the definition of an angle bisector
[tex]m < oab = \frac{1}{2} m < obd = \frac{1}{2} m < b[/tex]
Triangle AOB has measure 180 because it is a triangle,
and
the measure of triangle aob = 180 = (m < oab + m < obd) + m < aob = 55 + m < aob so the measure of angle aob = 125
