Henry devine bought a new dishwasher for $320. he paid $20 down and made 10 monthly payments of $34. what actual yearly interest rate did henry pay?

Henry paid a total of $360 for the dishwasher:  $20 + (10 x $34) = $20 + $340= $360

Therefore he paid $40 extra which we place over the original amount of the dishwasher:

Dividing 1 by 8 we get  .125 which, when changed to a percentage becomes 12.5%
Henry paid a yearly interest rate of 12.5%

Where’s the graph too show me?