A standard size pool cue is about 144 cm long. What is the length of a model of this pool cue with the scale factor 0.6?

I would have skipped the first stem and gone straight to 0.6*144cm

But it makes no difference.

So for this, set up a proportion.

$${\frac{{\mathtt{144}}}{{\mathtt{1}}}} = {\frac{{\mathtt{x}}}{{\mathtt{0.6}}}}$$

Cross-multiply to get the answer.

$${\mathtt{0.6}}{\mathtt{\,\times\,}}{\mathtt{144}} = {\mathtt{x}}$$

$${\mathtt{144}}{\mathtt{\,\times\,}}{\mathtt{0.6}} = {\mathtt{144}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{6}}}{{\mathtt{10}}}}\right)$$

Thus, the answer is 86.4