Yep another question... what my teacher never teach me this

Chandler was a caretaker at the state zoo. he noticed that the number of animals adopted by the zoo increased at a constant rate every year since 2010. which of the following graphs shows the slowest rate at which the animals in the zoo were adopted?

Which of the following is the result of expanding

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15