Which of these systems of linear equations has an infinite number of solutions?

a. 3x-8y=21
6x-16y=46

b. 3x+6y=22
6x+12y=44

c. 5x+9y=2-
10x-14y=48

d. 5x-9y=20
10x+18y=40

Liz is shipping a package to her friend.the maximum weight of a medium flat-rate box is 20 pounds,including the box which weighs 6 ounces.write and solve an inequality to describe the possible weight ,w, of the contents that liz will ship to her friend if she must use a medium flat-rate box.

You're locked out of your house. the only open window is on the second floor, 25 feet above the ground. there are bushes along the edge of the house, so you will need to place the ladder 10 feet from the house. what length ladder do you need to reach the window?

The candy store is having a 30% off sale. emma is going to buy $7.50 worth of candy.how much will she pay after the discount