Description for Correct answer:
3y + 9x = 54

=> 3 ( y + 3x ) = 54

=> 3x + y = \( \Large \frac{54}{3} \) = 18 .... (i)

and, \( \Large \frac{28x}{13y} = \frac{140}{39} \)

=> \( \Large \frac{x}{y} = \frac{140}{39} \times \frac{13}{28} \)

=> \( \Large \frac{x}{y} = \frac{5}{3} \)

=> 5y = 3x

=> 5y - 3x = 0 .... (ii)

Adding equations (i) and (ii), we get

3x + y + 5y - 3x = 18

=> 6y = 18

=> y = \( \Large \frac{18}{6} \) = 3

From equation (ii),

5 \( \Large \times \) 3 - 3x = 0

=> 3x = 15

=> x = \( \Large \frac{15}{3} \) = 5

\( \Large \therefore \) y - x = 3 - 5 = -2