Given the function f(x)=3x5\displaystyle {f{{\left({x}\right)}}}={3}{x}-{5}, 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}}}}=