Question

what should be added to twice the rational number -7/3to get 3/7?

Answer 1

Let the no be x
ATQ,
2×(-7/3)+x=3/7
-14/3+x=3/7
(3x-14)/3=3/7
21x-98=9
x=107/21

Answer 2

Let the rational number be $\frac{a}{b}$. 
Now, an equation can be formed. 
Solve and find the value of $\frac{a}{b}$. 
$2( \frac{-7}{3} ) + \frac{a}{b} = \frac{3}{7}$
$\frac{-14}{3} + \frac{a}{b} = \frac{3}{7}$
$- \frac{14}{3} + \frac{a}{b} = \frac{3}{7}$
$\frac{a}{b} = \frac{3}{7} + \frac{14}{3}$
$\frac{a}{b} = \frac{107}{21}$

∴ The required rational number is $\frac{107}{21}$.