Dropdown menu for calculations

Hello all! 

I am fairly new to Power BI and I have learned a lot from this community already! However, I am struggling a bit with a project I am working on, and hopefully someone here knows the answer. 

What I want to do is to make a calculation based on what value is chosen in the dropdown menu. I will explain in greater detail with this picture from Excel: 

If the cost per unit is 50, I want to multiply 50 by how many units is produced. If 3 units are produced the cost is (3x50) 150, if 10 units are produced the cost is 500. When the value in the dropdown menu is changed to for example 70, the total cost of producing 3 units will become (3x70) 210. 

I appreciate any help I could get on this,

Thanks