12p - 3 - 17p + 42

Combine "like" terms.

The -3 and 42 are both constants and combine to give 39.
The 12p and -17p are both linear terms (p to the first power times a constant coefficient) and combine to give -5p.

So, your expression simplifies to
-5p +39

To simplify the expression 12p - 3 - 17p + 42, we can combine like terms.

Step 1: Combine the terms with the same variable.
12p - 17p = -5p

Step 2: Combine the constant terms.
-3 + 42 = 39

Therefore, the simplified expression is -5p + 39.