how fast the water surface is rising when water is 18 inches deep in a trapezoidal through?

Question

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A trapezoidal trough is 10 feet long, 6 feet wide at the bottom, 12 feet at the top and 7 feet deep. If water flows in at the rate of 10 cubic feet per minute, find how fast the water surface is rising when water is 18 inches deep.

Answer 1

trof...18 inch=1.5ft, 1.5/7=0.214285714 or 21% av wae from bottom tu water level

delta-wide=6 ft....0.21485714*6ft=1.2857142857 ft

so, water surfus wide=6+1.28571428 ft=7.2857142857 ft

area=10ft*7.2857142857

=72.857142857 sq ft

dekta volume=10 ft^3/minut

delta rise=10/72.857142857=0.1372549 ft/minut  or 1.6470588 inch/minut

or 98.8235 inch/our