I can start by dividing 210 by the smallest prime number, which is 2. 210 divided by 2 is 105, so 210 = 2(105). Now I need to factor 105 further. I can try dividing it by the next prime number, which is 3. 105 divided by 3 is 35, so 210 = 2(3)(35). Next, I can try dividing 35 by the next prime number, which is 5. 35 divided by 5 is 7, so 210 = 2(3)(5)(7). 7 is already a prime number, so I don't need to factor it any more. I have found the prime factorization of 210, which is 2(3)(5)(7). To find the number of distinct prime factors, I just need to count how many different prime numbers appear in the factorization. I see that there are four distinct prime factors: 2, 3, 5, and 7. 
The number 74 can be factored as 2(37), so 74 is said to have two distinct prime factors. How many distinct prime factors does 210 have?