Answer:
[tex]k=\frac{2P}{x^2}[/tex]
Step-by-step explanation:
The formula is [tex]P=\frac{1}{2}kx^2[/tex]
We need to solve for [tex]k[/tex], so we can perform the steps shown below:
[tex]P=\frac{1}{2}kx^2\\P=\frac{kx^2}{2}\\2P=kx^2\\\frac{2P}{x^2}=k[/tex]
Hence, the third answer choice is correct.