(4b+2a)/(9b-6a)-(4a-6b)/(3a+6b)
=2(a+2b)/[-3(2a-3b)]-2(2a-3b)/3(a+2b)
=-2/3 ×[(a+2b)/(2a-3b)] -2/3 [(2a-3b)/(a+2b)]
=-2/3×2 -2/3×1/2
=-5/3