-20=-4x-6x
4x+6x=20
10x=20
x=20:10
x=2
proof:
-20=-4×2-6×2
-20=-8-12
(-8)+(-12)=-20
A or 20 means the angles are the same.
Again, a spreadsheet or suitable calculator makes this short work.
The sum is 184.
_____
The terms being summed are ...
2·3² +3 = 2·9 +3 = 18 +3 = 21
2·4² +3 = 35
2·5² +3 = 53
2·6² +3 = 75
Their total is
21 +35 +53 +75 = 184
Simplest fraction form is "3/4"
The combined volume of the two shapes is 3510 cubic inches.
To find the volume of each shape, use the formula: V = LWH.
The small shape is: 16 x 15 x 6 = 1350
The large shape is: 24 x 15 x 6 = 2160