ANSWER
The cost of a box of envelopes is $1.15
The cost of a box of paper is $2.45
Step-by-step 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)
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.