A Radar Receiver Indicates That a Pulse Return as an Echo

Multiple Choice

A radar receiver indicates that a pulse return as an echo in $20 \mu \mathrm { s }$ after it was sent. How far away is the reflecting object? $\left( c = 3.0 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s } \right)$

A) $6.0 \mathrm {~km}$
B) $9.0 \mathrm {~km}$
C) $3.0 \mathrm {~km}$
D) $1.5 \mathrm {~km}$