 
<translate> Mgbe Derek dị afọ isii, o nwere ụgbọala iri atọ n'ime ụgbọala iri atọ ndị o nwere n'oge ahụ. Afọ iri ka e mesịrị, mgbe Derek zụtasịrị ụgbọala 210 ọzọ, o nwere ụgbọala 210 + 30 = 240. Ebe ọ bụ na ọnụ ọgụgụ ụgbọala ji okpukpu abụọ karịa nke nkịta, Derek nwere nkịta 240 / 2 = 120 ugbu a. Azịza ya bụ otu narị na iri abụọ. <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. 