To find the distance \( d \) between points \( P \) and \( Q \) in a rectangular prism, we can use the 3D distance formula, which is given by:
\[ d = \sqrt{l^2 + w^2 + h^2} \]
where \( l \) is the length, \( w \) is the width, and \( h \) is the height of the prism.
Given:
- Length (\( l \)) = 12 cm
- Width (\( w \)) = 9 cm
- Height (\( h \)) = 18 cm
Now, we can substitute these values into the formula:
\[ d = \sqrt{(12)^2 + (9)^2 + (18)^2} \] \[ d = \sqrt{144 + 81 + 324} \] \[ d = \sqrt{549} \]
Now, calculate \( \sqrt{549} \):
\[ d \approx 23.4 \]
Rounding to the nearest tenth, the distance \( d \) between points \( P \) and \( Q \) is:
\[ \boxed{23.4} \text{ centimeters} \]