Hey there!
Here's your answer: m<BDC=69
Here's how I got it:<ADC=112; <ADB and <BDC together form <ABD.
you would add 6x+7and 12x-3 together to equal 112; 18x+4=112, and solve for x
next substitute 6 for x, into m<BDC=12x-3, and simplify!
Hope this helps!
