Answer
$15n^{4}-5n^{3}+40n$
Work Step by Step
$5n(3n^{3}-n^{2}+8)\qquad $...use the Distributive Property.
$=5n\cdot 3n^{3}-5n\cdot n^{2}+5n\cdot 8\qquad$
... multiply coefficients and add exponents.
$=15n^{1+3}-5n^{1+2}+40n\qquad... $simplify.
$=15n^{4}-5n^{3}+40n$
