How to add an "IF" date rule to a current formula?

I have a formula that is already written with a couple of "IF" rules and I am wanting to add to it. The current formula is 

=IIf([HW only]=No,[rent]*0.07613,IIf([state]="mo",[rent]*0.07613,0))

This formula works perfectly fine for what I need it to do at the moment, but I need to add to it. This is for orders that are written for my company, however, starting on October 1st we are getting a new tax rate. As you can see in the current formula, we have our current tax rate of 0.07613... I need to add an "IF" rule so that any new orders that we write up in our "Date Written" field of our program have a date of 10/1/2017 or later, they will have the new tax rate of 0.08113 applied to them.

Can anyone help me get this added to our current formula??

I tried:

=IIf([HW only]=No,[rent]*0.07613,IIf([state]="mo",[rent]*0.07613,0,IIf([date written]>=”10/1/2017”+0,[rent]*0.08113,0)))

But this tells me that the expression that I have entered contains invalid syntax.