indirectly means the same as inversely.
Because of typos in the question it’s not possible to tell which of the following is intended:
z=kr/(st), z=ks/(rt), z=kt/(rs)
so three answers will be given for the constant k.
360=kr/(st), 360=5k/36, k=36×72=2592;
360=ks/(rt), 360=12k/15, k=15×30=450;
360=kt/(rs), 360=3k/60, k=60×120=7200.