make operation

I did it, but I have a problem:

In the image if you see I have placed a mínimum in each field:

https://i57.tinypic.com/29x7qjp.jpg

154,50
500
90

And to give the result is not respectivo this… for example: if I put 100, in the field of 154,50 gives me another value, and the mínimum should be 154.50

Another thing, when I put 154.50 the value that the calculator should to give me has to be 154.50 and it is giving me another value.

How do I can do for someone to put him 154.50 achieves the same value as a minimum?

I don’t understand how to put it into the calculator

https://www.ads-software.com/plugins/calculated-fields-form/