Acrobat is calculating my form and doubling it.

i've created a form in Acrobat DC, for ordering supplies. the User may enter a number in the boxes and the should be automatically totaled in the bottom box. The bottom box is doubling everything. I have checked to make sure that each text box has only been represented once in the calculations. Its a super simple calculation of addition, yet i cannot find my error anywhere. Each box has no value until the user enters the value. can nayone help? i've attached the file