Given the function f(x)=2+6x2\displaystyle {f{{\left({x}\right)}}}=-{2}+{6}{x}^{{2}}, calculate the following values:
f(a)=\displaystyle {f{{\left({a}\right)}}}=  
f(a+h)=\displaystyle {f{{\left({a}+{h}\right)}}}=  
f(a+h)f(a)h=\displaystyle {\frac{{{f{{\left({a}+{h}\right)}}}-{f{{\left({a}\right)}}}}}{{{h}}}}=