We know that
• She placed 6 tiles on the first day.
,• By the end of day 4, she had placed 36 tiles.
Based on the given information, we can express the following equation.
[tex]y=3x+6[/tex]If she had placed 36 tiles in 3 days, it means she had placed 12 tiles per day, that's why the coefficient of x is 3. And the number 6 is the initial condition of the problem, that is, on day 0 she placed 6 tiles.
Now, for 100 tiles, we have to solve the equation when y = 100.
[tex]\begin{gathered} 100=3x+6 \\ 100-6=3x \\ 3x=94 \\ x=\frac{94}{3} \\ x=31.33333\ldots \end{gathered}[/tex]Notice that we cannot say 31 days, because it would be incomplete.