Hey there!
No numbers go into a prime number other than one and that number. 9 and 7 go into 63, so it’s not 63. 3 and 17 go into 51, so it’s not 51. 19 and 3 go into 57, so it’s not 57. That leaves 61. Nothing goes into this other than one and 61, so the answer is 61.
I hope this helps!