Let's use the formula:
1/T = 1/A + 1/B
where T is the time it takes for both Alina and Sophia to finish the job working together, A is the time it takes for Alina to finish the job alone, and B is the time it takes for Sophia to finish the job alone.
We know that:
T = 6 hours (since they can finish the job together in 6 hours)
A = 10 hours (since Alina can finish the job alone in 10 hours)
Now we can plug in these values and solve for B:
1/6 = 1/10 + 1/B
Multiplying both sides by 30B, we get:
5B = 3B + 15
Subtracting 3B from both sides, we get:
2B = 15
Dividing both sides by 2, we get:
B = 7.5
So Sophia can finish the job alone in 7.5 hours.
Hopes this helps!