Homework Help - Geometry Find the area of the thin sheeting required for making an open cistern (i.e.without a lid), $5$ m long, $3$ m wide,$ 4$ m deep. What does without a lid mean? I am not understanding.

There are four sides to the cistern. Two sides are $h\times \mathcal l: \;4\times 5 m^2$, two sides (ends) are $h \times w:\;4\times 3 m^2$, and the base is $\mathcal l \times w:\;5\times 3 m^2.$

Then add the area of the sides and the area of the base to obtain the total surface area that needs to be covered by the sheeting material:

$$2(4\cdot 5) + 2(4\cdot 3) + 5\cdot 3 = \text{ surface area of cistern}$$