Let e = Emil's age and r = Rosa's age.
e + r = 27 since Emil's and Rosa's ages added together make a sum of 27 years.
(e - 9) = 2r - 9 since Emil's age minus 9 (9 years ago) is two times what Rosa's age is minus 9 (9 years ago)
Since you can't be twice someone's age for only 1 year, Emil is still twice Rosa's age.
So e + r = 27 and e = 2r.
Even though we don't know what 2r is, if we plug it in for e, we can find out.
2r + r = 27
This means 2r + 1r = 27.
Now you can simplify this to find each person's age.
3r = 27
27 / 3 = 9
r = 9
2r = 18
e = 2r = 18
e = 18
r = 9
So Emil is 18 years old and Rosa is 9 years old.
