To find out who spent more time writing per problem, we need to calculate the unit rate (minutes per problem) for both Sonia and Maryna based on the data given.
**Sonia:**
- For 6 problems: \( \frac{120 \, \text{minutes}}{6 \, \text{problems}} = 20 \, \text{minutes/problem} \)
- For 18 problems: \( \frac{360 \, \text{minutes}}{18 \, \text{problems}} = 20 \, \text{minutes/problem} \)
- For 25 problems: \( \frac{500 \, \text{minutes}}{25 \, \text{problems}} = 20 \, \text{minutes/problem} \)
- For 60 problems: \( \frac{1200 \, \text{minutes}}{60 \, \text{problems}} = 20 \, \text{minutes/problem} \)
Sonia consistently spends **20 minutes per problem**.
**Maryna:**
- For 8 problems: \( \frac{200 \, \text{minutes}}{8 \, \text{problems}} = 25 \, \text{minutes/problem} \)
- For 15 problems: \( \frac{375 \, \text{minutes}}{15 \, \text{problems}} = 25 \, \text{minutes/problem} \)
- For 20 problems: \( \frac{500 \, \text{minutes}}{20 \, \text{problems}} = 25 \, \text{minutes/problem} \)
- For 50 problems: \( \frac{1250 \, \text{minutes}}{50 \, \text{problems}} = 25 \, \text{minutes/problem} \)
Maryna consistently spends **25 minutes per problem**.
### Conclusion:
Maryna spent more time writing per problem at the unit rate of **25 minutes/problem**.
Therefore, the correct answer is:
**Maryna spent more time writing per problem at the unit rate of 25 min. 1 problem.**