[" A string is strectched between fixed points separated by "],[75cm" .It is observed to have resonant frequated by "],[420Hz" and "315Hz" .There are no other resonant frequencies of "],[" between these two.Then,the lowest resonant frequencies "],[" for this string is "],[[" (a) "10.5Hz," (b) "105Hz],[" (c) "1.05Hz," (d) "1050Hz]]