Show steps as well please! I will mark brainiest

Answer:
4
Step-by-step explanation:
Alright we know the equation AB+BC=AC is the postulate formula given for AC length.
So we do algebraic equation here which would be
(4m-15)+(5m-6)=15
Remove parenthesis
4m-15+5m-6=15
Combine like terms:
9m-21=15
Add 21 to other side
9m=15+21
9m=36
Divide 9
m=36/9
m=4
So the last multiple choice there :)