Final answer:
By setting up a system of equations and substituting, we find that there are 8 cards that cost 35 cents each. Option b is the correct answer.
Step-by-step explanation:
The question asks to determine the number of 35 cent cards in a box, given the total price and a relationship between the number of 30 cent and 35 cent cards. To solve this, we can set up a system of equations. Let's denote the number of 35 cent cards as x and the number of 30 cent cards as y. According to the problem, we have the following equations:
- The total cost of the cards is $5.80: 0.35x + 0.30y = 5.80
- The number of 30 cent cards is six more than one half the number of 35 cent cards: y = 0.5x + 6
Insert the second equation into the first to find the value of x.
0.35x + 0.30(0.5x + 6) = 5.80
0.35x + 0.15x + 1.8 = 5.80
0.50x = 4
x = 8
So, there are 8 cards that cost 35 cents each in the box, which corresponds to option b.