 
<translate> A shekara shida, tare da karnuka sau uku fiye da motoci, Derek yana da 90 / 3 = motoci 30. Shekaru goma bayan haka, bayan ya sayi ƙarin motoci 210, Derek yana da motoci 210 + 30 = 240. Tun da yawan motoci sau biyu ne fiye da adadin karnuka, Derek a halin yanzu yana da karnuka 240 / 2 = 120. Amsar ƙarshe: 120. <eng> At six years old, with three times as many dogs as cars, Derek had 90 / 3 = 30 cars. Ten years later, after buying 210 more cars, Derek has 210 + 30 = 240 cars. Since the number of cars is twice as many as the number of dogs, Derek currently has 240 / 2 = 120 dogs. Final answer: 120. 