Taking speed of sound at 340 m/s
141 x 340/(340- 32.8) = 156.05 Hz
observer (vo) = 0 at rest at origin say
source (engine) vs = + 32.8 m/s > moving in + x direction
sound v = + 343 m/s > sound also reach observer + x direction
n' = heard frequency = n (real freq.) [v - vo] / [v - vs]
n' = 141 [343 - 0] / [343 - 32.8] = 155.91 Hz
***** you can use this formula always. keep all (v, vo, vs) in the same direction. if anyone is moving in opposite direction make it positive by using negative sign in formula for that. eg if sound is travellingbackwards, taken v = - 343
practice with this composite formula.
I will take 343m/sec. as speed of sound in air.
343 + 32.8 = apparent sound velocity of 375.8m/sec.
375.8/343 = 1.0956:1 ratio.
141 x 1.0956 = 154.48Hz.