To find the prime factorization of a number, divide it by the first number it can be divided by evenly. (Besides 1)
245/2? Nope
245/3? Nope
245/4? Nope
245/5? Yep!!
5 is the first number in the prime factorization of 245
245/5 = 49
49/2? Nope
49/3? Nope
49/4? Nope
49/5? Nope
49/6? Nope
49/7? Yep!!
7 is the second number in the prime factorization of 245
49/7 = 7
Since seven is a prime number it can only be divided by 1 and itself, so the third number in the prime factorization of 245 is 7. :)
The answer is 5 · 7 · 7, but since that's not one of the choices, the answer is 5 · 49 (Because 7 · 7 = 49)
The answer is A :)
Hopefully this helps! If you have any more questions or don't understand, feel free to DM me and I'll get back to you asap :)