Answer:
the mistake in this sentence (if the translation is what was supposed to be written) is the use of "los" in the sentence. The correct sentence should be "El auto es rapido" (with the accent on the a (sorry i can't remember how to type it))
Step-by-step explanation:
The word "los" should be used before a plural masculine noun, for los to be correct, the phrase would have to be "the cars are fast." = "Los autos son rapidos."
The word "el" should be used before a singular masculine noun, which is why it is the correct word for this phrase since only one car is being referred to