During one month, a grocery store sold 20% more chicken than fish by the pound. If the store sold 3,600 pounds of chicken during this month,

Call the pounds of fish sold,  F

So...the pounds of chicken sold  =  pounds of fish sold + 20% more  =  F  + .20F   ....so we have

F + .20F =  3600

1.20F  = 3600       divide both sides by 1.20

F  =  3000