Answer :
[tex]f(x)=\left\{ \begin{aligned}48\text{ for (0,3}\rbrack \\ \text{45 for }\lbrack4,8\rbrack\rbrack \\ 42\text{ for }\lbrack9,19\rbrack \\ 42,when\text{ x}>99\end{aligned}\right.[/tex]
Step 1
x=store charges
then
Step 2
$48 for each box of tiles when three or fewer boxes are purchased
[tex]\begin{gathered} f(x)=48,if0Step 3$45 for each box when 4 to 8 boxes are purchased
[tex]\begin{gathered} f(x)=45,if4\leq x\leq8 \\ f(x)\text{ = 45 for }\lbrack4,8\rbrack \end{gathered}[/tex]Step 4
$42 for each box when 9 to 19 boxes are purchased
[tex]\begin{gathered} f(x)=42,when9\leq x\leq19 \\ f(x)=42\text{ for }\lbrack9,19\rbrack \end{gathered}[/tex]Step 5
$38 for each box when more than nineteen boxes are purchased
[tex]f(x)=42,when\text{ x}>99[/tex]