A stack of colored cards is sorted such that x blue cards, y red cards, and z green cards are placed on top of each of a number of yellow cards, and there are no cards left over. How many yellow cards are there?
- The numbers of blue, red, and green cards placed on a given yellow card are in the ratio 3:4:7, respectively.
- A total of 90 blue cards, 120 red cards, and 210 green cards are placed.