An engine approaches a hill with a constant speed. When it is at a distance of 0.9 km , it blows a whistle whose echo is heard by the driver after 5 seconds. If the speed of sound in air is $330 \mathrm {~m} / \mathrm { s }$, then the speed of the engine is :\\
(1) $32 \mathrm {~m} / \mathrm { s }$\\
(2) $27.5 \mathrm {~m} / \mathrm { s }$\\
(3) $60 \mathrm {~m} / \mathrm { s }$\\
(4) $30 \mathrm {~m} / \mathrm { s }$