Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$28-25a+3a^2$
Using $(a+b)(c+d)=ac+ad+bc+bd$ or the product of $2$ binomials, the given expression, $(7-a)(4-3a)$, is equivalent to \begin{array}{l}\require{cancel} 7(4)+7(-3a)-a(4)-a(-3a) \\\\= 28-21a-4a+3a^2 \\\\= 28-25a+3a^2 .\end{array}