Asystem of linear equations could have an infinite number of solutions?

Find the slope of a line given the following two points

Which of the following can be used to explain a statement in a geometric proof?

Julie goes to the sports store and spends $40.50 before tax. she buys a pair of shorts for $21.75 and 3 pairs of socks that each cost the same amount. how much does each pair of socks cost? $$