"Let the answer be" \ A.
"Then:"
\qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad A \ = \ 18 + ( 8 * 9 )
\qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad = \ 18 + ( 72 )
\qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad = \ 18 + 72
\qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad = \ 90.
"So:"
\qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad A \ = \ 90.
"This is our answer."