[tex]\it a)\ \ x+y=98\ \ \ \ \ \ (*)\\ \\ \dfrac{x}{y}=\dfrac{2}{5} \Rightarrow\dfrac{x}{2}=\dfrac{y}{5}=\dfrac{x+y}{2+5}\ \stackrel{(*)}{=}\ \dfrac{98}{7}=14\\ \\ \\ \dfrac{x}{2}=14 \Rightarrow x=2\cdot14=28\\ \\ \\ \dfrac{y}{5}=14\Rightarrow y=5\cdot14=70[/tex]
