if estella continues to follow the same pattern of adding tiles, she will need tiles for the 100th row.

Explanation:

Step1: Identify the pattern

The number of tiles in row 1 is 1, row 2 is 3, row 3 is 5. The pattern is an arithmetic - sequence with first term $a_1 = 1$ and common difference $d=2$.

Step2: Use the arithmetic - sequence formula

The formula for the $n$th term of an arithmetic sequence is $a_n=a_1+(n - 1)d$. Here, $a_1 = 1$, $d = 2$, and $n = 100$. Substitute the values into the formula: $a_{100}=1+(100 - 1)\times2$.

Step3: Calculate the result

First, calculate $(100 - 1)\times2=99\times2 = 198$. Then, $a_{100}=1+198=199$.

Answer:

199