3x + 7y = 75 ........(i)
5x – 5y = 25 .........(ii)
In this example, we have to transform each equation to obtain the same numerical coefficient of one of the variables. To do this we multiply the first equation by 5 and the second equation by 7. Then, the variable y has the same coefficient.
x = \(\frac{550}{50}\) = 11
Putting x = 11 in (1), we get
3 × 11 + 7y = 75 \(\Rightarrow\) 33 + 7y = 75 \(\Rightarrow\) 7y = 75 – 33 = 42 \(\Rightarrow\) y = 6
\(\therefore\) x + y = 11 + 6 = 17.
