Let's use the variable x to represent the cost of one rose and y to represent the cost of one carnation.
If 8 roses and 5 carnations cost $31.75, we can write the following equation:
If 1 rose and 3 carnations cost $5.75, we can write a second equation:
From the second equation, we have x = 5.75 - 3y.
Using this value of x in the first equation, we have:
Now, calculating the cost of one rose, we have:
Therefore the cost of one rose is $3.50 and the cost of one carnation is $0.75.