*Sigh...If you really need me to do this for you, I will. It should have been obvious, but since you need me to write it out for you so you can see it in plain sight, here it is:
1. Causes always precede their effects in time
2. Therefore, causes require time in order to exist
3. There was no time prior to the Big Bang
4. Therefore, there was no cause to the Big Bang
If premise 1 is true, statement 2 logically and necessarily follows from 1. If premise 3 is true, than statement 4 follows from both 2 and 3.
You should be able to make these logical connections automatically in your head, without needing it to be written down as a formalized step-by-step argument format. Keep in mind that just because an argument isn't formalized, it doesn't mean the argument doesn't exist.