I guess it is a: seismic waves
Using lens equation;
1/o + 1/i = 1/f; where o = Object distance, i = image distance (normally negative), f = focal length (normally negative)
Substituting;
1/o + 1/-30 = 1/-43 => 1/o = -1/43 + 1/30 = 0.01 => o = 1/0.01 = 99.23 cm
Therefore, the object should be place 99.23 cm from the lens.
Time=50s
speed=25m/s
Distance = speed×time
=25×50
=1250m
DISTANCE TRAVELLED IS =1250m
Its actually C. I did the question on USA test prep and it said the correct answer was C.