do you convert feet to inches first before calculating area?

Since circumference is 9.5in then (C= π d) diameter is about 3 inches making the radius 1.5in

Area of each lid = π r² = 7.07 in² so two lids = 14.14in²

Lateral area = Circumference * height= 9.5*4.5= 42.75 in²

Each can 14.14 + 42.75 = 56.89 in²

56.89 * 1.05 = 59.73in² will be used for each can including the overlap allowance.

6 feet = 6*12= 72 in

80 feet= 80*12 = 960 in

Metal sheet Area = 72* 960 = 69,120 in²

69,120 /59.73 = 1157 whole cans wasting 12.39 in²

But this ignores the fact that each can will use a rectangular area of 9.5 (circumference straighted out) by 10.5 ( 4.5 + two 3in diameters, one at each end) then add 5% overlap in each direction you get a rectangle 9.975 by 11.025 for each can which gives you 109.97 in² per can

so 69,120 /109.97 = 628 whole cans wasting 58.84in²

is it 4 feet and 10 inches

Yes. You want all you measurements in the same unit.