Respuesta :

A straight line is 180°. So you can do:

(15x - 4) + (5x - 8) = 180  Simplify

20x - 12 = 180

20x = 192    Find the value of x

x = 9.6

m∠ABD = 15x - 4      Plug in x = 9.6

m∠ABD = 15(9.6) - 4 = 144 - 4 = 140°

m∠DBC = 5x - 8   Plug in 9.6

m∠DBC = 5(9.6) - 8 = 48 - 8 = 40°