To find the missing numbers represented by the two vertical bars (| |) in the equation, we need to solve for them based on the given proportion:

12 / x = 60 / 20

To solve for x, we can cross-multiply:

12 * 20 = 60 * x

240 = 60x

Now, isolate x by dividing both sides of the equation by 60:

x = 240 / 60

x = 4

So, the missing numbers represented by the two vertical bars are 4:

12 : 4 = 60 : 20