A closed cylindrical tin has radius 7 cm and its total surface area is $968{\text{cm}}^2$. Find its height in cm. Take π = 22/7.

Total surface = 2πr(r + h) = 2 × (22/7) × 7 × (7 + h) = 44(7 + h). Setting 44(7 + h) = 968 gives 7 + h = 22, so h = 15 cm. (Stopping at 22 reports r + h, not h — the same 22 comes from using only the curved surface 2πrh; 29 adds the radius instead of subtracting it; counting one flat end instead of two, 44h + 154 = 968, gives 18.5 cm.)