Can somebody explain to me what this subject is that's all i want to !

the restaurant bill you and your friend received was not itemized. you ordered 2 drink refills and the egg breakfast, for a total of $8.40. your friend ordered 3 refills and the egg breakfast for $9.35.
(a) write a system of equations for the situation. use r for the amount charged for a refill and b for the amount charged for the egg breakfast.
(b) graph the equations in the system.
(c) use your graph to estimate how much each item cost.