Answer:
60,466,176/117,649 or 513.9540157587399807903169597701637922974270924529745259203 decimal
Explanation:
Simplify the following: 
(6^5/7^3)^2 
 
7^3 = 7×7^2: 
(6^5/(7×7^2))^2 
 
7^2 = 49: 
(6^5/(7×49))^2 
 
7×49 = 343: 
(6^5/343)^2 
 
6^5 = 6×6^4 = 6 (6^2)^2: 
((6 (6^2)^2)/343)^2 
 
6^2 = 36: 
((6×36^2)/343)^2 
 
 | | 3 | 6 
× | | 3 | 6 
 | 2 | 1 | 6 
1 | 0 | 8 | 0 
1 | 2 | 9 | 6: 
((6×1296)/343)^2 
 
6×1296 = 7776: 
(7776/343)^2 
 
(7776/343)^2 = 7776^2/343^2: 
7776^2/343^2 
 
 | | | | 7 | 7 | 7 | 6 
× | | | | 7 | 7 | 7 | 6 
 | | | 4 | 6 | 6 | 5 | 6 
 | | 5 | 4 | 4 | 3 | 2 | 0 
 | 5 | 4 | 4 | 3 | 2 | 0 | 0 
5 | 4 | 4 | 3 | 2 | 0 | 0 | 0 
6 | 0 | 4 | 6 | 6 | 1 | 7 | 6: 
60466176/343^2 
 
 | | | 3 | 4 | 3 
× | | | 3 | 4 | 3 
 | | 1 | 0 | 2 | 9 
 | 1 | 3 | 7 | 2 | 0 
1 | 0 | 2 | 9 | 0 | 0 
1 | 1 | 7 | 6 | 4 | 9: 
Answer: 60466176/117649