Paul went to a solar panel store and paid $923.40 per solar panel for two solar panels and a flat rate fee for installation for a total of $1944.80. Brad went to another solar panel store and paid $940.50 per solar panel for two solar panels plus a per solar panel installation fee for a total of $1983.60. What is the difference in the amounts they paid in installation charges? A. $5.60 B. $4.60 C. $3.60 D. $6.60