Mathematical statistics: two-dimensional random variables

Boys, help a "blonde" to decide a task, please. I was tangled and does not know as correct to decide this task (Itwasntme).

The two-dimensional random variable $\displaystyle (X,Y)$ has a function of probability density $\displaystyle f\left( {x,y} \right) = \frac{a}

{{{\pi ^3}\left( {{x^2} + 3{y^2} + {x^2}{y^2} + 3} \right)}}$.

Find

a) the parametr $\displaystyle a$;

b) the function of a distribution $\displaystyle F\left( {x,y} \right)$;

c) the probability of hit of a casual point $\displaystyle \left( {X,Y} \right)$ in a square which is limited straight: $\displaystyle x=0$, $\displaystyle y=0$, $\displaystyle x=1$, $\displaystyle y=1$.