Hello from MrBillDoesMath!
Answer:
(3/4) a^(-5)b^(-3)c^2
Discussion:  
(18 a^-3b^2c^6)/ (24 a^2b^5c^4) =
(18/24) a^ (-3-2) b^(2-5) c^(6-4) =
                   as  a^-3/a^-2 = a ^ (-3-2) = a^(-5), for examples
(3/4) a^(-5)b^(-3)c^2
Thank you,
MrB
 
        
             
        
        
        
Note that the side adjacent to angle XYZ is given (6 cm) and that the hypo is also given (15 cm).  Thus, cos XYZ = adj / hyp = 6 cm / 15 cm  = 2/5 = 0.4.
XYZ is then  arc cos 0.4.  Use the arccos function on your calculator to determine XYZ and give XYZ in both degrees and radians.