Assuming that I am properly understand your question, all you have to do is get the initial values for each individual and add their savings monthly.
Starting
Josie: 80
Addie: 60
One month
Josie: 110
Addie: 100
Two months
Josie: 140
Addie: 140
So two months would be the answer.
You could also do...
x = months
80 + 30x = 60 + 40x
20 + 30x = 40x
20 = 10x (Divide by ten on both sides)
2 = x
2 Months