4(a+2b)-3(a-b)=4a+8b-3a+3b=a+11b
2/5 (a-b)-1/3 (2a+4b)+2/15 (2a+13b)=2a/5-2b/5-2a/3-4b/3+4a/15+26b/15
=(2a/5-2a/3+4a/15)+(-2b/5-4b/3+26b/15)
=0