Nevaeh went to the grocery store and purchased cans of soup and frozen dinners. Each can of soup has 400 mg of sodium and each frozen dinner has 600 mg of sodium. Nevaeh purchased a total of 7 cans of soup and frozen dinners which collectively contain 3600 mg of sodium. Graphically solve a system of equations in order to determine the number of cans of soup purchased, x, x, and the number of frozen dinners purchased, yy.