Is a diameter of circle O. If m∠ACB = 30°, what is m∠DBA? A. 30° B. 50° C. 60° D. 70° E. 90°

Every triangle equals 180 degrees, and we're trying to find the angle of DBA. So, we can identify DAB as a 90 degree angle to start. Then we can identify that ACB = ADB, meaning ADB is 30 degrees. With that information, we have this equation:

DBA = 180 - 90 - 30

DBA = 60