Need help with a selection criteria formula

Let me start by saying that I rarely ever work in CR11. I have a little issue with a selection criteria and I'm not really sure how to tackle it. The scenario is really simple and I suspect the solution is as well but for whatever reason I just can't wrap my head around it.

There's table called saleslines and a table called tasks. Salesline table as named contains all saleslines within a month time. The tasks table contains a list of contacts made by our sales team to the customers for a whole 12 months. Both tables linked by account number field. In my report I'd like to show saleslines that match sales order creation date to any contact date within 60 days before the SO creation date.

I'm not really sure how to write up this selection formula, I'd like to hear your thoughts on this. Thanks in advance!

Two fields in question. salesline.createddate and tasks.lastcontactdate

Ps. There could be multiple records in the tasks table that contain the same dates on same account numbers but with different task status, if that matters.