[tex]c.\quad 12:x = 16:8 \Rightarrow 12:x = 2 \Rightarrow 12 = 2\times x \Rightarrow x = 12:2 \Rightarrow \boxed{x = 6}\\\\~ \quad $ $ $ $x\times 10=80:2 \Rightarrow x \times 10 = 40 \Rightarrow x = 40:10 \Rightarrow \boxed{x = 4}\\ \\ ~\quad $ $ $ $x+x = 245 +x \Rightarrow 2x - x = 245 \Rightarrow \boxed{x=245}[/tex]
