Which is the property that justifies the action?

First off, the action would be to multiply both sides by 4. Since 4 is the reciprocal of 1/4, should multiply by that.

Then, Since we are multiplying it would be the multiplication property of equality, no tricks there.

Hope this helps!

A) Action: multiply both sides by 4. 

Have a look: 

(x/4)x4=16x4 
x=64 

As you can see, the value of x can be found by multiplying 4 on both sides.

Hope I helped :)