Suppose that $(X, B)$ is a $2-(v, k, \lambda)$ design. For $x \in X$, let $r_x$ be the number of blocks in $B$ containing $x$. Show that $r_x(k − 1) = λ(v − 1)$. Secondly, deduce that $r_x$ is independent of the choice of $x$, and this common value $r$ of $r_x$ satisfies the equation $vr = bk$.
I'm quite confused about how to begin this question. Any hints would be appreciated.