(1)3a/4b·16b/9a^2
=4/(3a)
(2)12xy/5a÷8x^2y
=(12xy)/(5a)·1/(8x^2y)
=3/(10ax)
(3)(-3xy)÷2y^2/3x
=(-3xy)·(3x)/(2y^2)
=-9x²/(2y)
(4)x+y/x-yx·yx-y/x+y
=(x+y)/(x-yx)·(yx-y)/(x+y)
=(xy-y)/(x-xy)