At a speed 343 m/s and frequency of 536 Hz;
the wavelength is computed by velocity / frequency = 343 / 536 = 0.640 m or 64 cm
If the tube is open at the top there is a concentrated at the top and a node at
the bottom at resonance.
i.e: at L = lambda / 4
The next resonance happens at 3 lambda/4 then 5 lambda/4 etc.
these resemble to 64 / 4 = 16 cm.
therefore,
the lengths from the open end to the water level corresponding to the first 2:
L1 = v / 4f = 343 / 4*536 = 16cm
L2 = 3v / 4f = 3*343 / 4*536 = 48 cm