Formules Calculation problems

I need help with 2 formules
This need to be in VBA and the formules can't be gone when chancing data.

1. Sheet 'Export FreshBooks' Unit Cost x Quantity the outcome must be on ''output'' F Factuurbedrag excl. BTW

2. this is to calculate TAX1
=(F/100)*'21






Test Version - Copy.xlsm