Answer
$8r^2+26rs-99s^2$
Work Step by Step
Using the $(a+b)(c+d)=ac+ad+bc+bd$ or the FOIL Method and the laws of exponents, the given expression, $
(2r+11s)(4r-9s)
,$ simplifies to
\begin{array}{l}\require{cancel}
2r(4r)+2r(-9s)+11s(4r)+11s(-9s)
\\\\=
8r^2-18rs+44rs-99s^2
\\\\=
8r^2+26rs-99s^2
.\end{array}
