Waves and Sound question bank (Physics)

A sonometer wire of resonating length $90 \mathrm{~cm}$ has a fundamental frequency of $400 \mathrm{~Hz}$ when kept under some tension. The resonating length of the wire with fundamental frequency of $600 \mathrm{~Hz}$ under same tension _____$\mathrm{cm}$.

A closed organ pipe $150 \mathrm{cm}$ long gives $7$ beats per second with an open organ pipe of length $350 \mathrm{cm}$, both vibrating in fundamental mode. The velocity of sound is ______ $\mathrm{m} {\mathrm{s}}^{-1}$.