[tex]\displaystyle a= \frac{5}{8} \cdot b \Rightarrow a=\frac{5b}{8} \\ a+b=130 \\ \frac{5b}{8} +b=130 \\ 5b+8b=130 \cdot 8 \\ 5b+8b=1040 \\ 13b=1040 \\ b= \frac{1040}{13} \\ b=80 \\ a+80=130 \Rightarrow a=130-80 \Rightarrow a=50 \\ a\cdot b=50 \cdot 80=4000 \\ a \cdot b =\boxed{4000}[/tex]
