Acircle is centered on point bb b b . points aa a a , cc c c and dd d d lie on its circumference. if ∠adc\orange{\angle adc} ∠adc start color #ffa500, angle, a, d, c, end color #ffa500 measures 61∘61^\circ 61 ∘ 61, degrees , what does ∠abc\blue{\angle abc} ∠abc start color #6495ed, angle, a, b, c, end color #6495ed measure? ∘^\circ ∘ degrees