Precalculus (6th Edition) Blitzer

$(-\infty, +\infty)$
Simplify the right side to obtain: $f(x) = 2(x) + 2(5) \\f(x) =2x+10$ This function is defined for all real number values of $x$, therefore its domain is the set of all real numbers. Thus, the domain is $(-\infty, +\infty)$.