How do I get the gross price from the net price?

For when the VAT rate was 17.5%, to get the amount before VAT you needed to divide by 1.175

Now the UK VAT rate is 20%, you need to divide by 1.2

Example:
If the price before VAT was £100, and VAT is 20%, then the price after VAT is £120.
So to work it out backwards: If you know the price after VAT is £120 and you want to know the price before VAT: £120 divided by 1.2 = £100

Hope that helps.