Answer :
let numbers be: x and y
x+y=3.9
x-y=0.9
Adding both
2x = 4.8
x = 2.4
2.4+y=3.9
y=3.9 - 2.4
y = 1.5
x+y=3.9
x-y=0.9
Adding both
2x = 4.8
x = 2.4
2.4+y=3.9
y=3.9 - 2.4
y = 1.5