Final answer:
After 3 days, Susanna and Alex will have spent the same amount.
Step-by-step explanation:
The relationship between Susanna and Alex's spending can be represented by the equation 8 - 1d = 11 - 2d, where d is the number of days. To find the value of d, we can solve the equation:
8 - 1d = 11 - 2d
Adding 2d to both sides:
d = 3
Therefore, after 3 days, Susanna and Alex will have spent the same amount.