991 is already prime. No tree is required.
991
The factor tree is as follows: 114 57,2 19,3,2
no
You cannot really make a factor tree for 7 because it is already a prime number.
No.
yes
13 is a prime number. It doesn't have a tree because its only prime factor is itself.
No you cannot. You might want to try the factor tree for 27.
Since 61 is already prime, a factor tree is not necessary. The prime factorization of 51 is 3 x 17, which wouldn't make much of a tree. More like a factor shrub.
35 5,7
15,3 3,5,3
prime factors