A counterexample proves something wrong. To disprove "When it rains, it pours," you could give an example of a time when it rains and does not pour. What if it only rains a little? What if it rains frogs? How are you supposed to "pour" frogs? I dunno. This is sort of an open-ended question. I'd go with "It drizzles, but does not pour."
Multiply 2 by 10, divide the answer by 5, and add 3 to the final answer
The slope would be 4.33. He sells 13 cars in 3 months, 13/3=4.33 cars each month. While you can't sell 4.33, remember that this is just the slope. The equation would be apprx y=4.33(x)
Flip the x and y like in the coordinate plane x,y not y,x