4. Find the greatest and least values of the expression $2 x+3 y$, if $(x ; y)$ are related by the relation $\sqrt{x-3}+\sqrt{y-4}=4$. For which $(x ; y)$ are they achieved?
Answer: $(2 x+3 y)_{\min }=37.2$ when $x=\frac{219}{25}, y=\frac{264}{25}, \quad(2 x+3 y)_{\max }=66$ when $x=3, y=$ 20.