Answer
$18cm$
Work Step by Step
The length of the cylinder submerged can be determined as:
We know that at equilibrium
$Kx+F_b=W$
$\implies Kx+\rho\cdot V_s\cdot g=mg$
We plug in the known values to obtian:
$(35+1000\frac{\pi}{4}(0.5)^2(10))x=1\times 10$
This simplifies to:
$x=18cm$