Simplify combining like terms:

– z2 + 13z2 – 5z + 7z3 – 15z

Dear Student

When term have the same algebraic factors, they are like terms.
Then,
= 7z^3+ (-z^2+ 13z^2) + (-5z–15z)
= 7z^3+ z^2(-1 + 13) + z (-5 - 15)
= 7z^3+ z^2(12) + z (-20) + 7z^3
= 7z^3+ 12z^2–20z + 7z^3

Thanks