For the following function, find $($a$)f(4),($b$)f(-\frac{1}{2}),($c$)f(a),$ and $($d$)f(\frac{2}{m}).$

$f(x)=4x^2-20x+25$

$($a$)$ Find the value of $f(4).$

$f(4)=$

$($Type an integer or a decimal.$)$