5a+2b=36
a/4=b/5=c/12=k
a=4k
b=5k
c=12k
5×4k+2×5k=36
20k+10k=36
30k=36
k=36/30
k=6/5
a=4×6/5
a=24/5
b=5×6/5
b=6
c=12×6/5
c=72/5
