s-s•3/7-(s-s•3/7)•3/8-75lei=25lei <=> (s-s•3/7)(1/1-3/8)=25lei+75lei <=> s(1/1-3/7)(8/8-3/8)=100lei <=> s(7/7-3/7)•5/8=100lei <=> s•5/7•5/8=100lei <=> s•5/7=100•8/5=20•8=160 <=> s=160•7/5=32•7=224lei.Deci a avut suma de 224lei.Un aparat de radio costa: 224•3/7=32•3=96lei,iar un tablou costa: (224-96)•3/8=128•3/8=16•3=48lei.