First find time taken to reach submarine
[tex]\\ \bull\tt\dashrightarrow t=\dfrac{80}{2}=40s[/tex]
[tex]\\ \bull\tt\dashrightarrow Distance=Velocity \times Time[/tex]
[tex]\\ \bull\tt\dashrightarrow Distance=1460(40)[/tex]
[tex]\\ \bull\tt\dashrightarrow Distance=58400m[/tex]
[tex]\\ \bull\tt\dashrightarrow Distance=58.4km[/tex]