Let the two numbers be x and y.
According to your question ;
x + y = 100
x - y = 30
Thus. x = y + 30
Substituting the value of x,
y + 30 + y = 100
2y + 30 = 100
y = 70 / 2 = 35
thus, y = 35
Substituting the value of y,
x + y = 100
x + 35 = 100
x = 100 -35 = 65
x = 65.
thus, the two numbers are 65 and 35.