VA IIMPLORR AJUTAȚI-MA !

[tex]\it m_{a.p.}\dfrac{11\cdot1+12\cdot1+13\cdot3+14\cdot7+15\cdot3}{1+1+3+7+3}=\dfrac{11+12+39+98+45}{15}=\\ \\ \\ =\dfrac{205}{15}=13,66[/tex]
[tex]\it \dfrac{205+15x}{15+x}=14 \Rightarrow 205+15x=14(15+x) \Rightarrow 205+15x=210+14x \Rightarrow \\ \\ \\ \Rightarrow 15x-14x=210-205 \Rightarrow x=5[/tex]