Ms. Jamieson is saving her money to buy a pair of boots to wear to the football game at the end of the month. The boots cost $69.99. The first week she saved $12.75. The second week she saved $16.50, and the third week she saved $21.75. How much money does Ms. Jamieson need to save the fourth week in order to have enough money to buy her boots?

To determine how much money Ms. Jamieson needs to save in the fourth week, we first need to calculate the total amount she has saved after the first three weeks, and then figure out how much more she needs to reach the cost of the boots, which is $69.99.

1. Calculate the total savings after three weeks:

   \[ \text{Total Savings} = \text{Week 1} + \text{Week 2} + \text{Week 3} \]

   Substituting in the amounts saved each week:

   \[ \text{Total Savings} = 12.75 + 16.50 + 21.75 \]

2. Perform the addition step by step:

   • First, add Week 1 and Week 2: \[ 12.75 + 16.50 = 29.25 \]

   • Then, add that result to Week 3: \[ 29.25 + 21.75 = 51.00 \]

   Thus, after three weeks, Ms. Jamieson has saved a total of $51.00.

3. Next, determine how much more she needs to save in the fourth week to afford the boots:

   \[ \text{Amount Needed} = \text{Cost of Boots} - \text{Total Savings} \]

   Substituting the values we know:

   \[ \text{Amount Needed} = 69.99 - 51.00 \]

4. Calculate the amount needed:

   \[ 69.99 - 51.00 = 18.99 \]

Therefore, Ms. Jamieson needs to save $18.99 in the fourth week to have enough money to buy the boots.