Given the function f(x)=\displaystyle {f{{\left({x}\right)}}}=5x+7\displaystyle {5}{x}+{7}

(a) find and simplify f(x+3)\displaystyle {f{{\left({x}+{3}\right)}}}
(b) find and simplify f(x)+3\displaystyle {f{{\left({x}\right)}}}+{3}
(c) find and simplify f(x)+f(3)\displaystyle {f{{\left({x}\right)}}}+{f{{\left({3}\right)}}}