Physic
posted by SB .
What are the three longest wavelengths for standing sound waves in a 124cmlong tube that is (a) open at both ends and (b) open at one end, closed at the other?

You have to do some thinking. An open end gives a reflection of zero degrees, add that to two half wavelengths of 1.24m.
A closed end gives 180 degrees phase shift, so 1.24m is now only 90 degrees to give a full wavelength for the round trip.
I will be happy to critique your thinking. 
how do i go from degree to meter...answer is required in m.

360 degrees is one wavelength. So count the reflection (either 0 deg,or 180 deg ..1/2 wavelength), then the two paths of 1.24m which provide the rest of the shift.

part A i used the equation n*(lambda/2)=length, for n 1,2, and 3. this is coming back as incorrect

I would put 1.24 in for length and solve for the three wavelengths, that is what it asked.

now i am confused ...dont know where to begin