Write the following sets in roster from:
E = {x : x is a prime number, which is a divisor of 42}.
Prime number = Those number which is divisible by 1 and the number itself.
Prime numbers are 2, 3, 5, 7, 11, 13, …
Divisor of 42:
42 = 1 × 42
42 = 2 × 21
42 = 3 × 14
42 = 6 × 7
So, divisors of 42 are 1, 2, 3, 6, 7, 14, 21, 42
The elements which are prime and divisor of 42 are 2, 3, 7
So, E = {2, 3, 7}