HELP IM CONFUSED I WASNT AT SCHOOL

How do i do this using elimination 2x+3y=12 x-y=6

To complete your spring schedule, you must add calculus and physics. at 9: 30, there are three calculus sections and two physics sections; while at 11: 30, there are two calculus sections and three physics sections. how many ways can you complete your schedule if your only open periods are 9: 30 and 11: 30?

What is the difference between regular convex and concave polygons