Apencil at a stationery store costs $1, and a pen costs $1.50. stefan spent $7 at the store. he bought a total of 6 items. which system of equations can be used to find the number of pencils (x) and pens (y) he bought? x + 1.5y = 7 x + y = 6 1.5x + y = 7 x = 6y x + 2y = 7 6x = 1.5y 2x + y = 7 6x = 1.5y