The cross section of a canal is a trapezium in shape. If the canal is 7 metres wide at the top and 9 metres at the bottom and the area of cross-section is 1280 square metres, find the length of the canal.	Choose the correct answer:
A) 160 metres	B) 172 metres	C) 154 metres	D) 165 metres	E) None of these
None of these   Let the length of canal = h m.   Then,area of canal = 1⁄2 × h(9 + 7)   or 1280 = 1⁄2h(16)   ∴ h = 1280×2/16=160m   160 metresnswer 160 metres
<result>A</result>
The cross section of a canal is a trapezium in shape. If the canal is 7 metres wide at the top and 9 metres at the bottom and the area of cross-section is 1280 square metres, find the length of the canal.