Find -x + 10 less than 0.

0
-x + 10
x - 10

This is an inequality.

-x + 10 < 0
    - 10     - 10   deduct 10 from both sides
-x         < -10
÷ -1         ÷ -1      divide both sides by negative 1.
  x         > 10        notice that when you divide x by a negative number, the inequality sign is reversed. from < to >.

The value of x is greater than 10.

Let us assume that x = 11

-x + 10 < 0
-11 + 10 < 0
-1 < 0 

31 is prime. and it’s prime factorization is just 31.