Marco is studying a type of mold that grows at a fast rate. He created the function f(x) = 345(1.30)x to model the number of mold spores per week. What does the 1.30 represent? How many mold spores are there after four weeks? Round your answer to the nearest whole number.

1.30 represents the number of mold spores Marco had at the beginning of the study; 985 mold spores
1.30 represents the number of mold spores grown in a given week; 448 mold spores
1.30 represents the 30% rate of weekly growth; 345 mold spores
1.30 represents the 30% rate of weekly growth; 985 mold spores