Final answer:
Macy and Robby will have the same amount in their accounts after 4 weeks.
Step-by-step explanation:
To find out when Macy and Robby will have the same amount in their bank accounts, we can set up an equation. Let's say the number of weeks is 'x'.
For Macy: The amount she saves each week is $12.50, so her total savings after 'x' weeks would be 12.50x.
For Robby: The amount he saves each week is $7.50, so his total savings after 'x' weeks would be 20 + 7.50x.
To find when they have the same amount, we can set up the equation: 12.50x = 20 + 7.50x. Solving this equation, we get x = 4.
Therefore, after 4 weeks, Macy and Robby will have the same amount in their accounts.