x=3, y=2. x=1, y=2. x=4, y=3. x=12, y=4. x=12, y=21. x=5, y=7. x=5, y=2. x=18, y=6. x=3, y=2. x=3, y=2. x=7, y=8. x=8, y=−2. x=a(a−b), y=b(a+b). [2]Ejercicio66. A, $520; B, $440. 23 y 17. 20 y 16. Terciopelo, $6; seda, $3. Trigo, $1; centeno, $45. Té, $12; café, $14. Caballo, $92; vaca, $64. [5]Ejercicio67. 37. 1325. 320. 521.