The information given below relates to Wasp Ltd. which manufactures a single type of chemical. Overhead processing costs for the last thirteen accounting months (of four weeks each) have been as follows:

Period	Overhead cost	Output
	Sh. 000	000 tonnes
1 2 3 4 5 6 7 8 9 10 11 12 13	770 820 810 830 960 900 940 950 940 870 800 820 790	120 150 160 170 200 170 200 200 180 160 140 150 140

Required:

Devise a formula to assist in predicting the overhead budget for the thirteen months. (15 marks)