Alrighty, the sum of all the angles of a quadrilateral, as you might know, is 360 degrees. So since you're given all the 3 angles, you can find the 4th one by subtracting the sum of all the 3 angles from 360.
[tex]360 - (98 + 72 + 105)[/tex]
which when evaluated gives,
[tex]360 - 275 = 85[/tex]
Now that's the interior angle not the exterior. To get the exterior we need to subtract the angle from 180 which gives:
[tex]180 - 85[/tex]
which evaluates to [tex]95[/tex].
Here's the diagram if needed :P
