Answer
Please see the work below.
Work Step by Step
We know that according to law of conservation of energy
$(\frac{1}{2})mv^2=(\frac{1}{2})Kx^2$
This simplifies to:
$x=\sqrt{\frac{m}{K}v}$
We plug in the known values to obtain:
$x=(\sqrt{\frac{35000}{2800000}})(7.5)=0.84m$
