Show text only if date record added is less than 150 days from another date in database

I have two date fields in my database, one is a date which is manually added (StagingDate) and the other is a timestamp which records when the record is added (DateAdded). I'm using a Show If to display text only if a record has been added 150 days or less before the StagingDate. I have the following syntax, and I want to add in a "+150 days" to the DateAdded bit but I'm suffering from "code blindness" because I can't get the syntax right! Can you help? Something like this:

<?php if(date("Y-m-d", strtotime($row_WADAclients['StagingDate'])) < date("Y-m-d", strtotime($row_WADAclients['DateAdded']"+150 days"))) { // Show if column... ?>

Text to display

<?php } // Show if column... ?>