Vibrating a 75g Bungee Cord: Standing Wave Formation

[strikingleafs01]

Homework Statement

A 75 g bungee cord has an equilibrium length of 1.20 m. The cord is stretched to a length of 1.80 m, then vibrated at 20 Hz. This produces a standing wave with two antinodes.

Homework Equations

I really am not sure how to approach this using an equation, tried to use

w = sqrt (k/m)

The Attempt at a Solution

using the above equation I got a value of

1184 N/m for 'k', which is incorrect

 

[strikingleafs01]

i'm getting now double of that, and half of that value, anyone have any ideas still? this assignment is due 12:00pm tomorrow for us