The cross-section of a canal is shown in figure (iii) given below. If the canal is 8 m wide at the top and 6 m wide at the bottom and the area of the cross-section is 16.8 m², calculate its depth.

Consider ABCD as the cross section of canal in the shape of trapezium.

Draw a perpendicular AM from A to CD.

So, AM is the depth of canal.

Given, the area of cross-section of canal = 16.8 m².

∴ $\dfrac{1}{2}$ × sum of parallel sides × depth = 16.8

⇒ $\dfrac{1}{2}$ × (AB + DC) × AM = 16.8

⇒ $\dfrac{1}{2}$ × (6 + 8) × AM = 16.8

⇒ $\dfrac{1}{2}$ × 14 × AM = 16.8

⇒ AM = $\dfrac{16.8 \times 2}{14}$

⇒ AM = $\dfrac{33.6}{14}$ = 2.4 m

Hence, depth of canal = 2.4 meters.