Please explain this step by step, i struggled to understand this paragraph, thanks a lot, how did the percent change figure comes from? As i wish to find out how the percentage figure was 3 percent change of stock and then it changes by the 30 percent?

As with other investment, there is a form of accelerator effect that affects the demand for durable goods and, for this reason, purchases of durable goods are more volatile than other components of private consumption expenditure. Con- sumers with higher incomes want more cars per family, or cars of better quality. Suppose, for simplicity, that the demand for cars is proportional to income, so a 3 percent increase in income increases the desired stock of cars by 3 percent, and assume that cars depreciate at a rate of 10 percent. Then the demand for cars is closely related to the growth of income. To see this, note that if income is constant and the stock of cars is at the desired level, the demand for cars arises only because cars depreciate and have to be replaced. in such a situation, purchases of new cars correspond to 10 percent of the stock. But if income increases by 3 percent in a year. car purchases increase by an amount corresponding to 3 percent of the stock. This is a 30 percent increase in the demand for new cars. in fact, purchases of durable goods contribute a great deal to uctuations in aggregate consumption. Demand for food is a much more stable component of aggegate demand