Answer:
12 hours
Step-by-step explanation:
Given data
Steve= 4 hours
Steve and Andrea= 3 hours
Applying the combined work formula
1/A+1/B= 1/T
1/4+1/B= 1/3
solve for B
B+4/4B= 1/3
cross multiply
3(B+4)= 4B
3B+12= 4B
12= 4B-3B
12= B
Hence Andrea will spend 12 hours alone
