Question 1038578
Let n=7 cent stamps. Then 3-cent equals n-5, and 12-cent equals n/2. So.
7n+3(n-5)+12(n/2)=273
7n+3n-15+6n=273
16n=288
n=18 7-cent stamps, 13 3-cent stamps, 9 12-cent stamps!!!!!!!!!!!!!!!!