how to calculate GST in calc

hello all this is my first post
so recently ive been tasked to create a invoice template for a new company and ive downloaded this template from libreoffice.org and im trying to replace the Discount % section with GST so we can automatically add the GST to the customers bill.
my question is what should i put in place of sections f33 and f34 to add a percent from the line total?
thanks

In F33 put the GST percentage rate, e.g. for Australia 10 (percent). Simply change F35 to

=IF(F32+F34=0;"0.00";F32+F34)

So you add the amount as GST rather than subtracting a discount.

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