Question 1103252
the trapezoid is presumably an isosceles trapezoid.
this means both legs are the same length.
if the lower base is 3 inches and the upper base is 5 inches, this means that the upper base extend 2 more inches on each side of the height of the trapezoid.
this forms a right triangle where the base is 1 inch and the base angle is 78 degrees.
you can find the length of the height by taking tan(78) = height / base.
solve for the height to get height = base * tan(78) = 1 * tan(78) = 4.704630109 inches.
area of the trapezoid is 1/2 * height * (b1 + b2) = 1/2 * 4.704630109 * 8 = 18.81852044 square inches.
volume of the gutter is length of the gutter times the area of the trapezoid = 120 * 18.81852044 = 2258.222453 cubic inches.
here's my picture.
not the best picture in the world, but hopefully good enough to show you what i mean.
<img src = "http://theo.x10hosting.com/2017/120101.jpg"alt="$$$">
here is also a link to an online calculator that you can use to check your work.
<a href = "https://www.easycalculation.com/area/volume-of-trapezoidal-prism.php" target = "_blank">https://www.easycalculation.com/area/volume-of-trapezoidal-prism.php</a>