To find out how much Sierra will have saved after 4 weeks, we can use the expression based on the information given. The expression for the total amount saved after \( w \) weeks is:
\[ \text{Total Savings} = 45 + 3w \]
Where \( 45 \) is the initial amount from her aunt, and \( 3w \) is the amount she saves each week.
Now, let's substitute \( w = 4 \) into the expression:
\[ \text{Total Savings} = 45 + 3(4) \] \[ = 45 + 12 \] \[ = 57 \]
After 4 weeks, Sierra will have saved a total of $57.00.
Thus, Sierra will save $57.00 after 4 weeks.