How would i find the missing angle in this if i only have the exterior angle and one adjacent angle?

You have to find angle BCA which would be 180-124 (this is because angle BCA is on a 180 line and your given the exterior angle) so it’s
56
Then to find the missing angle subtract 56 and 100 from 180( cause all internal angles of a triangle equal 180)
180-100-56
24 would be the answer

Hope this helps :D