With an installment buying plan you take possessions of the item and with a layaway plan you take possession of the

Answer for the first blank: immediately
Answer for the second blank: when the item is fully paid for

Installment plans are basically loans where you pay a fixed payment (usually each month) to pay back the amount loaned, which is the principal, plus interest. Layaway is where you do the same thing but there isn't any interest. You simply break up the price of the item into smaller reasonable chunks. The pro of a layaway plan is that there is no interest, but as mentioned above, the con is that you don't get the item til it's fully paid off. 

For a 0.25 pfor b o.3pp (0.25+0.3)=0.28