Numerical Analysis problem

Determine the step h and the minimum number of nodes in a table of values equidistants of the function $\displaystyle f(x)=\sqrt{x} $ between 1 and 2, if we use a quadratic interpolation and we want 7 correct digits.

It's not a quadratic spline interpolation. I think it can be done with Newton or Lagrange interpolation. If n is the number of nodes, then $\displaystyle h=1/n$. I don't really know how to start the problem. Isn't by finding an inequality with f(x)-p(x)<0,0000001 ?

Any useful help will be VERY appreciated.