7(5a-2b)^2+2|4b-3c|=0
7(5a-2b)^2=0,5a-2b=0,a=2/5b
2|4b-3c|=0,4b-3c=0,c=4/3b
a:b:c=2/5b:b:4/3b=6:15:20