Problem $6$: $(11\%$ of Assignment Value$)$

Some physics students are studying periodic motion using an oscillating mass on a spring. After collecting data, they sketched the position versus time graph

The function that represents the data on the graph may be written as

x$=$Acos$(\backslash$omega t$+\backslash$phi $),$ with $,\backslash$phi in$[0,2\backslash$pi $)$

If the mass is $2\mathrm{.}37$ kg $,$ then what is the spring constant, in newtons per meter?