Answer:
x - 4
Explanation:
The volume V is calculated as
V = lbh
Given 2 of the dimensions
(x - 1)(x - 3) = x² - 4x + 3
Then the third dimension is found by dividing V(x) by x² - 4x + 3
Using long division
x - 4
-----------------------------------------
x² - 4x + 3 | x³ - 8x² + 19x - 12
x³ - 4x² + 3x
-------------------------------------
- 4x² + 16x - 12
- 4x² + 16x - 12
--------------------------------------
0 ← remainder
Thus quotient = x - 4
That is the missing dimension is x - 4