(a-2b)/(a+2b)=3
a-2b=3a+6b
2a=8b
a=4b
a+2b/a-2b+3a-6b/4a+8b=(4b+2b)/(4b-2b)+(12b-6b)/(16b+8b)=6/2+6/24=3+1/4=13/4