Respuesta :

[tex]3a + b = 7\Leftrightarrow 3(3a + b) = 3 \times 7\Leftrightarrow 9a + 3b = 21 \: (1)\\ 6x + 8y = 40\Leftrightarrow \frac{2(3x + 4y)}{2} = \frac{40}{2} \Leftrightarrow 3x + 4y = 20 \: (2) \\ (1),(2)\Rightarrow 9a + 3b > 3x + 4y[/tex]

[tex]\bf \begin{array}{lll|llll} 3a+b&=&7&&6x+8y&=&40\\&&&&&\\ 3(3a+b)&=&3(7)&&\frac{1}{2}(6x+8y)&=&\frac{1}{2}(40)\\&&&&&\\ 9a+3b&=&21&&\frac{6x}{2}+\frac{8y}{2}&=&\frac{40}{2}\\&&&&&\\ 9a+3b&=&21&&3x+4y&=&20 \end{array}\\\\ ~\hspace{7.5em}21>20[/tex]