To find what BDC is, you first have to solve for x. You can do this by creating an equation because you know what ADC equals:
6x + 7 + 12x - 3 = 112
18x - 4 = 112
+ 4
18x = 116
÷ 18
x = 6.44
Now you can substitute in 6.44 to find BDC:
12 × 6.44 = 77.33
77.33 - 3 = 74.33°, which is your answer. I hope this helps!
