a) (2^4)^3 x 4^6 : 8^5 = 2^12 x (2^2)^6 : (2^3)^5 = 2^12 x 2^12 : 2^15 = 2^(12+12-15) = 2^9
b) 3^7 x 3^8 x 3^9 : (3^5)^4 = 3^(7+8+9) : 3^20 = 3^24 : 3^20 = 3^(24-20) = 3^4
c) (7^12)^5 : 7^16 : 49^5 = 7^60 : 7^16 : (7^2)^5 = 7^(60-16) : 7^10 = 7^44 : 7^10 = 7^(44-10) = 7^34
d) (5^4)^7 x 25^5 : 5^30 = 5^28 x (5^2)^5 : 5^30 = 5^28 x 5^10 : 5^30 = 5^(28+10-30) = 5^8