(12) (10xy^3) (3x^2y^2) (5x) (2y)
= mmmmh
= 3600 x^3 y^6
For the next 4, I showed you how to do these.
Did you read my reply?
[(a^2bc^4)(ab^3c^2)]^2 / (b^2c^5)^3
= [a^3 b^4 c^6]^2 / (b^6 c^15)
= (a^6 b^8 c^12) / (b^6 c^15)
= a^6 b^2 / c^3