Let f(x)=6x25x+8\displaystyle {f{{\left({x}\right)}}}={6}{x}^{{2}}-{5}{x}+{8}. Find the following:
f(a)=\displaystyle {f{{\left({a}\right)}}}=  
2f(a)=\displaystyle {2}{f{{\left({a}\right)}}}=  
f(2a)=\displaystyle {f{{\left({2}{a}\right)}}}=  
f(a+2)=\displaystyle {f{{\left({a}+{2}\right)}}}=  
f(a)+f(2)=\displaystyle {f{{\left({a}\right)}}}+{f{{\left({2}\right)}}}=