(a.) is the answr. ............................................
1. Factor the expression 

2. Since
is placed in the denominator of the given expression, then 
3. Now the expression can be simplified:

Hi there
dollar amount of each monthly payment is interest
11,798.81÷120
=98.32
percent of the total payments is total interest
(11,798.81÷41,798.81)×100
=28.23%
Hope it helps