Answer:
17
Explanation:
< ABD = <ABC + < CBD
Substitute in what we are given
87 = 9x-1 + 6x+58
Combine like terms
87 = 15x +57
Subtract 57 from each side
87-57 =15x +57-57
30 = 15x
Divide by 15
30/15 =15x/15
2=x
We want to find <ABC
<ABC = 9x-1
= 9*2-1
=18-1
=17