If f(x)=x2+3x4\displaystyle {f{{\left({x}\right)}}}={x}^{{2}}+{3}{x}-{4}, simplify each of the following.

f(x+h)\displaystyle {f{{\left({x}+{h}\right)}}} =  

f(x+h)f(x)\displaystyle {f{{\left({x}+{h}\right)}}}-{f{{\left({x}\right)}}} =