Sandwiches and juice

[kate]

John, Peter and Mary decided to buy sandwiches and juices. John bought three sandwiches and two juices for 1,40$. Peter bought two sandwiches and five juices and paid 1,40$. Mary bought one juice and one sandwich.
a) What is the price of the sandwich and of the juice?
b) How much did Mary paid?
c) How much did the three of them paid?