a=12x
b=12y
c=12z
12x.4=12y.6=12z.15
=>48x=72y=180z
=>\(\frac{x}{\frac{1}{48}}\)=\(\frac{y}{\frac{1}{72}}\)=\(\frac{z}{\frac{1}{180}}\)=k
=>x=\(\frac{k}{48}\);y=\(\frac{k}{72}\);z=\(\frac{k}{180}\)=>k=BCNN=720
=>x=\(\frac{1}{48}\).k=\(\frac{1}{48}\).720=15
a=12.15=180