First of all, 6 and 10 are not prime numbers as they both have at least two pairs of factors (one factor pair plus one and itself).
Anything multiplied by two is even. Therefore, a) 2 counterexamples the statement. Just to show why 7 doesn't work, seven multiplied by 3 is 21, which is odd, and 7 times 7 is 49, and 7 times 5 is 35 (all prime multipliers). The only one that works is two.
