1) you are given frequency. Wavelength/2 = Length for fundamental. Therefore wavelength is 2L
You know that v = (f)(λ) or cycle/s * cm/cycle = cm/s
2) With 5 antinodes, you have 5 half wavelengths, so 5/2 λ = L (solve for λ)
f for this standing wave is v from part (1) divided by new λ
or you can use the fact that this is the fifth harmonic so f5 = 5f1