in general as you rise in numbers the amount of prime numbers decrease becasue more and more numbers are able to go into it. for the case of the 90s 90,92,94,96, and 98 are out becuase they are even and 2 goes into them. then 95 becasue it is a multipleof 5, 93 and 99 because of mulitples of 3 and 91 becasue 7 times 13 equals 91. so the only number left is 97. if you need help further just let me know.