First, you need to find the greatest common factor, and because we are factoring out the minus sign, it should be a negative number.
For -1 & 30, the GCM is -1, and using the GCM, we can factor each of them out:
-1 30
/ \ / \
-1 x 1 -1 x 30
Then, we can use distributive property to factor out the minus with the GCM outside of the parentheses:
-1 + 30 =
-1(1 + 30)