Answer: 71/7
Explanation:
No picture is provided so I am assuming that BD is an angle bisector.
1. ∠ABD=10x-7, ∠DBC=3x+5 Given
2. ∠ABD = ∠DBC Definition of angle bisector
3. 10x-7 = 3x+5 Substitution
4. 7x - 7 = 5 Subtraction Property of Equality
5. 7x = 12 Addition Property of Equality
6. x = 12/7 Division Property of Equality
7. ∠ABD = 10(12/7) - 7 Substitution
8. ∠ABD = 71/7 Adding like terms