A function f is defined by $f(x)=x^2$ what is the value of $y$ if $y$ is a positive integer such that $\large\frac{1}{2}$$f(y)=6$ ?

Question

$\begin{array}{1 1} (a)\; 7 \\ (b)\; 4 \\ (c)\; 6 \\ (d)\;12 \end{array}$