Noel devine bought a new dishwasher for $320. he paid $20 down and made 10 monthly payments of $34. what actual yearly interest rate did noel pay? a. 29.09% b. 68.75% c. 14.55% d. 34.38%
i know i'm making this harder than it needs to be, but i really don't understan. can you explain how to get the answer? !

IN finding the interest we need to use the following formula:
 Interest= Principal x Rate x Time  or I= PRT
Substitute values: I= [$20 + ($10 x $34)] -320 =$40
P= $320
R=?
T=10 months/year
I=PRT
Since R is a missing term, we will solve for R using this formula: R=I/PT
R=  [$20 + ($10 x $34)-320] / ($320 x 10 months)
                                          T=10 months÷12 months=0.83
R= ($40)/ $320 X 0.83
R= 40/ 265.6
R=15.06024096