a + b = 70
a =
[tex]a + b = 70 \\ a = \frac{3}{7} \times b \\ \frac{3}{7} b + \frac{7}{7} b = \frac{10}{7} b = 70 \\ = > \frac{10}{7} b = \frac{70}{1} \\ = > b = \frac{70 \times 7}{10} = \frac{490}{10} = 49 \\ = > a = 70 - b \\ = > a = 70 - 49 \\ = > a = 21[/tex]
