Diego is buying shrimp and rice to make dinner. Shrimp costs $6.20 per pound and rice costs $1.25 per pound. Diego spent $10.55 buying shrimp and rice. The relationship between pounds of shrimp `s`, pounds of rice `r`, and the total cost is represented by the equation `6.20s+1.25r=10.55`. Write an equation that makes it easy to find the number of pounds of rice if we know the number of pounds of shrimp purchased.