vaibhav was writing the CAT exam.there were four passages of equal length(in words)and they had 5,8,8and 6 questions respectively.Vaibhav can answer exactly 12 questions in the time he takes to read any one of four passages.Assume that his rate of reading and answering questions remains the same across all four passages.By what percentage should Vaibhav increase his speed(reading)in order to cutdown his total time spent by 10% ?

1) 20%
2) 18.5%
3) 25%
4) 15%
5) 15.625%