The function $y=x^{2}$ has been transformed to $y=a f(b x) .$ Determine the equation of each transformed function.
a) Its graph is stretched horizontally about the $y$ -axis by a factor of 2 and then reflected in the $x$ -axis.
b) Its graph is stretched horizontally about the $y$ -axis by a factor of $\frac{1}{4},$ reflected in the $y$ -axis, and then stretched vertically about the $x$ -axis by a factor of $\frac{1}{4}$.