do the math on press

[Kano]

Hi there,

Wanting to add a button to my form so when the user selects it the grand total input value = all input values whos name is index of "subtotal_".

 

Have tried many other ways of achieving this but with no success so I think this is the best way to get the totals. The subtotal_ is a value gotten using javascript (price * qty(<select>).

 

Can any one help?

 

thanks.