Answer
$3x^2+11x-20$
Work Step by Step
Using $(a+b)(c+d)=ac+ad+bc+bd$ or the Distributive Property, the given expression, $
(3x-4)(x+5)
,$ is equivalent to
\begin{array}{l}\require{cancel}
3x(x)+3x(5)-4(x)-4(5)
\\\\=
3x^2+15x-4x-20
\\\\=
3x^2+11x-20
.\end{array}