Remark
You have a trapezoid on the face closest to us. The first thing you must do is find the height. After you have done that, you find the area of the face. Then you can find the volume.
Step One.
Find the small space between the end of the perpendicular and the end of the line marked 3.9 cm.
That space = (6 - 4)/2 = 2/2 = 1
Step Two
Find the height
Use the Pythagorean theorem
a^2 + b^2 = c^2
a = 1
b = ???
c = 3.9
1^2 + b^2 = 3.9^2
1 + b^2 = 15.21 Subtract 1 from both sides.
b^2 = 15.21 - 1
b^2 = 14.21 Take the square root of both sides.
sqrt(b^2) = sqrt(14.21)
b = 3.7696 b and h are the same thing.
h = 3.7696
Step 3
Find the area of the Trapezoid.
h = 3.7696
b1 = 4
b2 = 6
Formula
A = (b1 + b2)*h/2
Sub and Solve
A = (4 + 6)*3.7696/2
Area = 10* 3.7696/2
Area = 18.85 cm^2
Step 4
Find the volume
V = B * h
B = 18.85
h = 8 cm
Volume = 18.85 * 8 = 150.78 cm^3