4. Find the greatest and least values of the expression $2 x+y$, if $(x ; y)$ are related by the relation $\sqrt{x-1}+\sqrt{y-4}=2$. For which $(x ; y)$ are they achieved?
Answer: $(2 x+y)_{\max }=14$ when $x=5, y=4,(2 x+y)_{\min }=\frac{26}{3}$ when $x=\frac{13}{9} y=\frac{52}{9}$.