Suppose that f(x,y)=x+3y\displaystyle {f{{\left({x},{y}\right)}}}={x}+{3}{y} at which 5x5,5y5\displaystyle -{5}\le{x}\le{5},-{5}\le{y}\le{5}.

Absolute minimum of f(x,y)\displaystyle {f{{\left({x},{y}\right)}}} is  
Absolute maximum of f(x,y)\displaystyle {f{{\left({x},{y}\right)}}} is