b)
[tex] \it |2x+7| =9 \Rightarrow 2x+7=\pm9 \Rightarrow 2x+7\in\{-9,\ 9\}|_{-7} \Rightarrow2x \in \{-16, \ 2 \}|_{:2} \Rightarrow\\ \\\Rightarrow x\in \{-8,\ \ 1\} [/tex]
c)
[tex] \it 4x-5y=25 \Rightarrow 4x = 25 +5y \ \ \ \ \ (1)\\ \\ 25+5y\in M_{5} \stackrel{(1)}{\Longrightarrow} 4x \in M_{5}\ \ \ \ (2)\\ \\ |x| <12 \stackrel{(2)}{\Longrightarrow} x\in\{\pm10,\ \pm5,\ 0\} \Rightarrow x\in \{-10,\ -5,\ 0,\ 5,\ 10\} \ \ \ \ \ \ (3) [/tex]
[tex] \it (3) \Rightarrow 4x \in\{-40,\ -20,\ 0,\ 20,\ 40\} \stackrel{(1)}{\Longrightarrow} 25+5y\in\{-40,\ -20,\ 0,\ 20,\ 40\}|_{-25}\Rightarrow\\ \\ \Rightarrow 5y \in \{-65,\ -45,\ -25,\ -5,\ 15\}|_{:5}\Rightarrow y\in\{-13,\ -9,\ -5,\ -1,\ 3\} \ \ \ \ \ (4) [/tex]
[tex] \it (3),\ (4) \Rightarrow (x,\ y) \in\{(-10,\ -13),\ (-5,\ -9),\ (0,\ -5),\ (5,\ -1),\ (10,\ 3)\} [/tex]
