Answer:
a=21, b=24, c=27
Step-by-step explanation:
a= side 1, b= side 2, c= side 3
a+b+c=72
a/b=7/8 and b/c=8/9 (proportion it)
then cross multiply to get 8a=7b and 9b=8c---> divide to get a=7/8b and c=9/8b
put that into the first equation--> 7/8b+8/8b+9/8b=72
add the fractions to get 24/8b=72 (24/8 equals 3) so 3b=72 (divide to get b=24)
then fill that in to the above equations (8a=7b, 9b=8c)
8a=7(24) and 9(24)=8c---> 8a=168 and 8c=216
divide all that and get a=21 and c=27
with all the measurements, you can check the proportion to make sure it works (7:8:9-->21:24:27)
if you multiple 7, 8, and 9 by 3 then you get the numbers found so it works
