The text mentions a product of two terms and a subtraction. The first term is the number - 13 times the difference of c and d. As a mathematical expression, this would be
[tex](-13)\times(c-d)[/tex]Expanding this expression using the distributive rule, we have
[tex]\begin{gathered} (-13)\times(c-d) \\ =-13c+13d \end{gathered}[/tex]