Estimating Form - How to Adjust Pricing by Quanitities

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I have an estimating access db, with a form to select equipment installation tasks quantities, and price per item selected are calculated according to material, contractor, and labour rates input previously in another table. The problem I face is that I my labour rates are dependent upon the quantity of equipment installation tasks. Any help on how to develop this aspect would be appreciated. The other option would be to create multiple equipment installation tasks with quantity amounts. I.e under 200 meters use this task id, over 200 and under 500 use this... etc. I would rather be able to put a formula together to calculate the cost based on quantity and possibly other factors like resources required. I've attached the beginning of the database. Thanks!