2 dependent dropdowns that then autopopulate a specific cell

Hi

I need a macro/formulae that first creates dependant dropdowns in cells B1 & B2 of the 'Dropdowns' sheet based on the data on the 'Tables' sheet of the attached file - and then when choices have been made for each dropdown this then autopopulates cell B4. Also, if choices have then been changed for the first dropdown (cell B1), then cell B4 should clear until the new selection for the second dropdown is made in B2.

Also, these should be dynamic dropdowns so that if I change the source data the dropdowns automatically update with the new data.

I think this probably needs a macro, but if it can be done with formulae/tables then even better.

Would appreciate some help.

Thanks.