Given the function f(x)=\displaystyle {f{{\left({x}\right)}}}=6x2\displaystyle -{6}{x}-{2}

(a) find and simplify f(x7)\displaystyle {f{{\left({x}-{7}\right)}}}
(b) find and simplify f(x)7\displaystyle {f{{\left({x}\right)}}}-{7}
(c) find and simplify f(x)+f(7)\displaystyle {f{{\left({x}\right)}}}+{f{{\left(-{7}\right)}}}