The students in Mr Black's Spanish class are reading the same 500-page book. Four students Anna, Jason, Charle, and Ben, are in the class. Anna reads a page in 30 seconds, Jason reads a page in 40 seconds, Charle reads a page in 25 seconds and Ben reads a page in 50 seconds. If Ben and Anna both read the whole book, Ben will spend how many more seconds reading than Anna?