If your total requires more than just adding things together (multiplication, division, or subtraction), you will need to use the Calculation Field (rather than just using the Total Field).
This may be as simple as multiplying your final total by 1.2 to show the amount payable including VAT but there are many other clever options here to allow for almost all calculations.
To include an element from your form, enter a square bracket [ , and then a list of all possible elements that can be included in the calculation will appear underneath where you are typing. Ignore any fields you don't need, like the Stall frontage measurement.
Click one to add it to your calculation. You should use brackets in the same way you would in any sum. You do not need an = sign and spaces are OK.
For example, to work out how much to charge the applicant for their £12 parking tickets including VAT, you would write [Parking tickets] * 12 * 1.2
Tip: By typing the first square bracket, [ Radio Group, Checkbox Group and Dropdown List totals will also appear in your list for selection