Let L represent letters
Let B represent bills
Let M represent Magazines
Let A represent Ads
From the question;
If they receive three more bills than magazines implies that
[tex]B=M+3[/tex]If they receive the same number of letters as magazines implies
[tex]L=M[/tex]If they receive five more ads than bills, it implies that
[tex]\begin{gathered} A=B+5 \\ \text{Thus, since }B=M+3 \\ A=M+3+5=M+8 \end{gathered}[/tex]Recall that, the sum of all the mails is 15, i.e
[tex]L+B+M+A=15[/tex]Substitute the values of L, B, and A in terms of M to find the value of M
[tex]M+M+3+M+M+8=15[/tex]Collect like terms
[tex]\begin{gathered} M+M+M+M+3+8=15 \\ 4M+11=15 \\ 4M=15-11 \\ 4M=4 \end{gathered}[/tex]Divide both sides by 4
[tex]\begin{gathered} \frac{4M}{4}=\frac{4}{4} \\ M=1 \end{gathered}[/tex]If, M =4, Find the number of L
[tex]\begin{gathered} \text{ Recall,} \\ L=M \\ \text{Thus,} \\ L=1 \end{gathered}[/tex]Hence, they receive 1 letter