Answer:

First, put the ratio in lowest terms: 3 Corollas to 2 Camrys to 1 Avalon.

Now, think of a "group" of cars as containing 3 Corollas, 2 Camrys, and Avalon.  Thus, each group comprises 6 cars.  Since Toyota manufactured 6240 cars, you can surmise that the company made 6240/6 = 1040 groups of six cars.

Each of these 1040 groups contains 3 Corollas, for a total of 3*1040=3120 Corollas.

Each of these 1040 groups contains 2 Camrys, for a total of 2*1040=2080 Camrys.

Each of these 1040 groups contains 1 Avalon, for a total of 1*1040=1040 Avalons.