The following data relates to Nyota ltd which possesses a type of chemical. The overhead cost for the last 13 account periods is as follows; Period 1 2 3 4 5 6 roa 9 10 11 (X) Output in units shs. 120 150 160 170 200 170 200 200 180 160 140 150 140 (Y) overhead cost Shs 770 820 810 830 960 900 940 950 940 870 800 12 13 Required Device a formula to assist in the calculation of the overhead budget for the 13 period 820 790