Wrong amount is being displayed in Calculation field

a users has called me today as the amount to pay in the form is coming up incorrect is certain options are chosen

http://form.jotformeu.com/form/50576074514354?

what have i done wrong?

each options is £50 so if 6 options chosen it should say £300 its says £500

You need to assign first Calculation Values to the Checkboxes options so that they will be calculated properly as numbers by the Calculation widget

user guide: -How-to-Assign-Calculation-Value

You can test my demo form where I have it setup correctly http://form.jotformpro.com/form/50978926993983?

Inform us if you need further assistance.

Thanks.