Question

the sum of two numbers is 10 in the difference is 3

Answer 1

X + Y = 10

X - Y = 3

adding [1] & [2]

2X = 13

X = 13/2

X = 6.5

Put X = 6.5 in first eq

6.5 + Y = 10

Y = 10 - 6.5

Y = 3.5

I hope your concept is clear