5ab^3*(-3a^3b/4)*(-2ab^4c/3)
=[5*(-3/4)*(-2/3)]a^(1+3+1)b^(3+1+4)c
=5/2a^5b^8c
(-2x^my^n)(-x^2y^n)^2(-3xy^2)^3
=(-2x^my^n)(x^4y^2n)(-27x^3y^6)
=[(-2)*1*(-27)]x^(m+4+3)y^(n+2n+6)
=54x^(m+7)y^(3n+6)
正确答案如上,