The motion of a car on a position-time graph is represented with a horizontal line. what does this indicate about the car’s motion?

If the line on the graph is horizontal, the car is at the same position no matter what time you look at it.  That means that the car is sitting motionless in one place, and not moving.  The car's speed, velocity, and acceleration are all zero, although its resale value may be decreasing.

because growing process had stoped after 4-5 year

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form