How do I calculate String mass density from what I got frequency= 30.0Hz, segment length= 42.5cm , nodes=2, string length=83.5cm and tension=2.150kN?

2 nodes along the string or just at the ends?

If just at ends then wavelength = 2 * L = 2*0.835
look at
http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/string.html

note if third harmonic, two nodes along string then f = 3 * fundamental f
If nodes at both ends and two along the string then wavelength = .75 * L
= .75*0.835