Without a calculator!

Both of machines and time are doubled. Thus total toy cars produced will be, $2\times 2\times 10=\color{#0C6AC7} {\boxed {40}}$ .

If it takes ten machines ten minutes to make ten toy cars,

it will take twenty machines 10 minutes to make 20 toy cars as the number of machines is doubled

but if the time is doubled the number of toy cars will be doubled too

so 20 * 2 = 40

$\large 2\times 2\times 10 = 40$

They are doubled

To solve this problem, find out how many toy cars each machine makes in the first example:

Number of Cars Produced / Number of Machines = Cars per Machine, in 10 minutes

10 / 10 = 1

Now, for the new scenario:

Number of Cars Produced / Number of Machines = Cars per Machine, in 10 minutes

x / 20 = 1 * 2

Rearrange:

x = 20 * 2

x = 40