ANSWER
The cost of a box of envelopes is $1.15
The cost of a box of paper is $2.45
EXPLANATION
Define Variables:
Let 'e' represent a box of envelopes
Let 'p' represent a box of papers.
System of Equations:
3e + 4p = 13.25 ...........................(equ 1)
2e + 6p = 17 ...........................(equ 2)
[tex]\begin{gathered} (\text{equ 1) }\times-2\Rightarrow-6e\text{ -8p = -26.5 }\ldots\ldots..(equ\text{ 3)} \\ (\text{equ 2) }\times3\text{ }\Rightarrow\text{ 6e + 18p = 51 }\ldots\ldots\ldots\ldots..(equ\text{ 4)} \\ \text{ -----------} \\ \text{ 0 e + 10p = 24.5} \\ p\text{ = 2.45} \end{gathered}[/tex][tex]\begin{gathered} \text{Substitute the value of 'p' into (equ 1)} \\ 3e\text{ + 4p = 13.25} \\ 3e\text{ + 4(2.45) = 13.25} \\ 3e\text{ + 9.8 = 13.25} \\ 3e\text{ = 13.25 - 9.8} \\ 3e\text{ = 3.45} \\ e\text{ = }\frac{3.45}{3} \\ e\text{ = 1.15} \end{gathered}[/tex]Answer as a sentence
Hence, the cost of a box of envelopes is $1.15 and the cost of a box of paper is $2.45.