I read that one example of k3 surface is a double cover of $\mathbb{P}^2\mathbb{C}$ ramified over a sextic. My question is why a sextic? i believe that the sextic is isomorphic to the ramification divisor, but why is this? also how can i see that k3 surfaces realized this way are deformation equivalent? 
thank you



k3 surface as ramified double cover of $\mathbb{P}^2$
**Q1:** Hurwitz formula + canonical divisor of $\mathbb P^2$.


**Q2:** Move the curve in $\mathbb P^2$.


