Conditional Format - cell color according to value in second cell

Hi.

I have been reading the forum for a while now and I just can't seem to figure out this simple problem. I have two columns of data. In B, I have an inventory item number. In column D, I have a value that represents the age of that item (how long it has been on the shelf). What I want to do, is color the item number cell (column A); green, yellow, red depending on its age (column B). Green is 30 days or less, yellow is 60 days or less, and red is anything over 60 days. I have tried using the conditional formatting rules and I have failed repeatedly..... Can anyone help? I have attached a simple example if that helps.

Thanks,

Craig