17) -6b(2b²+5b⁵ – bc²) =

$$-6b(2b^2+5b^5 - bc^2) = -6b \cdot 2b^2 - 6b \cdot 5b^5 - 6b \cdot (-bc^2) = -12b^3 - 30b^6 + 6b^2c^2$$