"Двадцять одна машина"
двадцять перша. You need to agree the word for "first" (перший) with a gender of a noun it refers to
*Twenty one machines" was correct, but does машина also mean "machines"? Not only "Cars"?
I dont understand why it end with "ина" if it is plural and more than five objects, shouldnt it be ended in "ини"?