You have the following populations in two different years:
year 1952 -> population = 2,933,200
year 1958 -> population = 2,932,300
The previous information can be considered as a pair of points in the coordinate plase, in which you have a function that determines the population dependeing of the year.
To know the rate of increasing or decreasing of the population, you calculate the slope of the fuction. You use the following formula:
m = (y2 - y1)/(x2 - x1)
(x1,y1) and (x2,y2) are two points of the function. In this case you can take (x1,y1) = (1952, 2,933,200) and (x2,y2) = (1958, 2,932,300). By replacing in the formula for the slope m youhave:
m = (2,932,300 - 2,933,200)/(1958 - 1952)
m = -900/6 = -150
Then, the slope of the function is -150. This means that the population is decreasing (minus sign) at a rate of 150 people per year.