See the same question here.
https://www.jiskha.com/questions/1823034/a-sample-of-seawater-taken-from-the-atlantic-ocean-freezes-at-2-14-c-and-a-sample
A sample of seawater taken from the Atlantic Ocean freezes at –2.14 °C and a sample from the Arctic Ocean freezes at –1.96 °C. Assume i = 2.
3 answers
How do I solve for Kf?
You are supposed to know Kf. I think that is 1.86 C/m