In a particular very small region, the consumer price index, C, depends on the current value of gross regional domestic expenditure E, number of people living in poverty P. and the average number of household members in a family F, by the following formula: C=100+ e-EP/F If it is known that the gross regional domestic expenditure is decreasing at a rate of PHP 50 per year, and the number of people living in poverty and the average number of household members in a family are increasing at 3 and 1 per year, resp., how fast does the consumer price index change per year at the moment when E = 1,000, P = 200, and F= 5?