Answer:
In 2013 there were approximately 2.2 million cars for sale.
Step-by-step explanation:
Since the number of cars is decreasing by 23% per year, it is a decay model. This types of decay can be expressed in the following expression:

Where x is the year, cars(2007) is the number of cars in 2007. Applying this data we have:

If we want to know the number of cars in 2013, we need to apply that value to x and solve the expression.

In 2013 there were approximately 2.2 million cars for sale.
49,98,147,196,245,294,343,392,441,490,539,588,637,686,735,784,833,882,931,980,1029,1078,1127,1176,1225,1274,1323,1372,1421,1470,1519,1568,1617,1666,1715,1764,1813,1862,1911,1960,2009,2058,2107,2156,2205,2254,2303,2352,2401,
Rate is the change in one variable in relation to another variable. Generally, rate is calculated as follows:
R = ΔV1/ΔV2
Where
R = Rate
ΔV1 = Change in variable 1
ΔV2 = Change in variable 2
In the current scenario,
ΔV1 = 250,000 m^3 of mulch applied
ΔV2 = 1 m^2 of garden space
Therefore,
Rate of applying much is, R = 250,000/1 = 250,000 m^3/m^2