Answer:
15km
Step-by-step explanation:
[tex] \rm \mapsto \: {9}^{2} + {12}^{2} = {x}^{2} \\ \rm \mapsto \: {x}^{2} = 81 + 144 \\ \rm \mapsto \: {x }^{2} = 225 \\ \rm \mapsto \: x = \sqrt{225} \\ \rm \mapsto \: x = 15[/tex]
