s=steve's dog's weight
i=ian's dog's weight
so steve's dog weighs 5 times of ians dog
s=5 times i
s=5i
total weight=72
s+i=72
we can subsitute 5i for s since s=5i
5i+i=72
add
6i=72
divide by 6
i=12
find s
s+i=72
s+12=72
subtract 12
s=60
weighs 60 pounds