Find and completely reduce an expression for the slope of the line passing through the given points:

 (x1,y1)=(20,400)\displaystyle {\left({x}_{{1}},{y}_{{1}}\right)}={\left({20},{400}\right)} 

 (x2,y2)=(t,t2)\displaystyle {\left({x}_{{2}},{y}_{{2}}\right)}={\left({t},{t}^{{2}}\right)} 

m=\displaystyle {m}=