Both represent the same thing, just written in a different format.
======================================================
Work Shown:
1/8 = 0.125
12 & 1/8 = 12 + 1/8 = 12 + 0.125 = 12.125
1/4 = 0.25
1 & 1/4 = 1 + 1/4 = 1 + 0.25 = 1.25
The block has dimensions: 4 in by 1.25 in by 12.125 in
The volume of a rectangular block is the product of the length, width and height.
volume = length*width*height
volume = 4*1.25*12.125
volume = 60.625
Let's convert the result to a mixed number
60.625 = 60 + 0.625
60.625 = 60 + 625/1000
60.625 = 60 + (5*125)/(8*125)
60.625 = 60 + 5/8
60.625 = 60 & 5/8
Using a calculator, note that 5/8 = 0.625
The units for the volume are in cubic inches
(inch)*(inch)*(inch) = (inch)^3 = cubic inches