3x + 7y = 75 ..(i)
5x - 5y = 25
∴ x - y = 5 ...(ii)
On multiplying Eq. (ii) by 7 and adding to Eq. (i), we get
3x + 7y = 75
7x - 7y = 35
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10x = 110
x = 11
∴ Putting the value of x in Eq. (ii), we get
11 - y = 5
∴ y = 6
∴ x + y = 6 + 11 = 17
