Christina's age will be half of 80 in five years to come, meaning in five years, Christina's age will be 1/2*80=40 years.
If in five years Christina will be 40, currently she is 40-5=<<40-5=35>>35 years old.
Oscar will be 3/5 times as old as Christina is now in 15 years, meaning he will be 3/5*35=<<3/5*35=21>>21 years old in 15 years.
Currently, Oscar is 21-15=<<21-15=6>>6 years old.
#### 6