Vlookup function

i believe that the anwers are provided to the practice activities, which would anser my quesion, but here is my question nonetheless:

It relates to question 3 of Unit 2 Pactice activity. I could not work out how to keep the cells blank until a product code is selected. the formula i used, which did not work was:

=VLOOKUP(IF(A16<>" ",A16," "),Product_list,3,FALSE)

I was trying to say that, if there was no blank, then give me the value in that cell, otherwise give me a blank. this did not work.

Also, i was looking for the function 'ISBLANK', which used to return an empty cell, but this did not appear when i searched through the available functions.