Answer:
6m²-m²+5m-1
Step-by-step explanation:
Polynomial 1 = m³ + 3m² - 18m
Polynomial 2 = 23m - 4m²
Polynomial 3 = 5m³ - 1
(m³+3m²-18m)+(23m-4m²)+(5m³-1)
When adding polynomials, you'll add like terms.
(m³+5m³)+(3m²-4m²)+(-18m+23m)+(-1)
(6m³)+(-m²)+(5m)+(-1)
6m³-m²+5m-1
