A bungee jumper, whose mass is 98 kg, jumps from a tall platform. After reaching his lowest point, he continues to oscillate up and down, reaching...

A bungee jumper, whose mass is 98 kg, jumps from a tall platform. After reaching his lowest point, he continues to oscillate up and down, reaching the low point two more times in 9.0 s. Ignoring air resistance and assuming that the bungee cord is an ideal spring, determine its spring constant.