Solution to 4.

 

Ross will argue with Rachel if either Rachel takes too long or Joey doesn't get ready. If Chandler and Joey don't get ready, then the taxi will leave unoccupied. But the taxi will not leave unoccupied. Therefore, if Chandler gets ready then Ross won't argue with Rachel.

Simple statements:

A = Ross will argue with Rachel.

L = Rachel takes too long.

J = Joes gets ready.

C = Chandler gets ready.

U = The taxi will leave unoccupied.

Substituting:

 

A if either L or not-J

If not-C and not-J, then U.

Not-U.

Therefore, if C then not-A

 

These are easy to symbolize:

(lv~j)->a

(~c&~j)->u

~u

.:c->~a