Please help with #12

ACD = 76

Step-by-step explanation:

The sum of the interior angles of a triangle total 180 degrees.

The sum of the two angles making up a straight line also total 180 degrees.

In the triangle, we have A + B + C = 180.

On the straight line, we have C + = 180, so C = 180 -

We now have A + B + (180 - ) = 180

A + B - = 0

(4x + 15) + 21 - (7x + 6) = 0

3x = 30

x= 10

Therefore ACD = 7x + 6 = 76

b

step-by-step explanation: