Answer 1

Let the depth of canal bed.
Given:
Lengths of the parallel sides of the trapezium shape canal are 10 m and 6 m.
\And, the area of the cross section of the canal is 72 m².
Area of trapezium \[=\frac{1}{2}\times(\text{ Sum of the parallel sides })\times(\text{ Perpendicular distance between the parallel sides })\]
\[72 = \frac{1}{2} \times (10+6)\times (d)\]
\[72 = 8\times d\]
\[d =\frac{72}{8}= 9 m\]