The only way I know how to do this one is to get a list of all the two-digit prime numbers (go to: http://www.math.utah.edu/~pa/math/primelist.html -- they are all in the first row of the data presented). Then divide each of them by 7 and count the ones that have a remainder of 2. If you are using your calculator, you will get a decimal fraction when you divide by 7 (you are only dividing into primes, so none of them will come out even). If the decimal fraction begins .285714, then you know you have a remainder of 2. This isn't as onerous as it seems, since there are only 21 two-digit primes.
