The ratio of income of 2 …

Let the common ratio term of income be x and expenditure be y.
So, the income of first person is Rs.9x and the income of second person is Rs.7x.
And  the expenditures of first and second person is 4y and 3y respectively.
Then, Saving of first person =9x - 4y
and  saving of second person = 7x - 3y
As per given condition
 9x - 4y = 200
 {tex}\Rightarrow{/tex} 9x - 4y - 200=0    ... (i)
and, 7x - 3y = 200 
{tex}\Rightarrow{/tex} 7x - 3y - 200 =0   ..... (ii)
Solving equation (i) and (ii) by cross-multiplication, we have 
{tex}\frac { x } { 800 - 600 } = \frac { - y } { - 1800 + 1400 } = \frac { 1 } { - 27 + 28 }{/tex}
{tex}\frac { x } { 200 } = \frac { - y } { - 400 } = \frac { 1 } { 1 }{/tex}
{tex}\Rightarrow{/tex} x =200 and y =400
So, the solution of equations is x = 200 and y = 400.
Thus, monthly income of first person = Rs.9x = Rs.(9 {tex}\times{/tex} 200)= Rs.1800
and, monthly income of second person = Rs.7x = Rs.(7{tex}\times{/tex} 200)= Rs. 1400