To find the total number of miles Chris walked, multiply the number of miles she walked per day by the number of days she walked.

$\text{Total miles} = 4 \, \text{miles/day} \times 21 \, \text{days}$

$\text{Total miles} = 84 \, \text{miles}$

Chris walked 84 miles in all.

Would you like more details or have any questions?

Here are 5 questions related to this problem:

1. What if Chris walked 5 miles a day for 21 days? How many miles would she walk?
2. How many miles would Chris walk if she walked 4 miles a day for 30 days?
3. If Chris took a break for 3 days, how many miles did she walk in 18 days?
4. What if Chris increased her distance to 6 miles a day for the next 10 days? What would be the new total?
5. How many weeks did Chris walk for 21 days?

Tip: Multiplication is a quick way to find totals when you have repeated addition scenarios, like daily walking over multiple days.