#### Answer

$7+2(x+9)$
$=7+(2x+18)\quad $(distributive property)
$=7+(18+2x)\quad $(addition: commutative property)
$=(7+18)+2x\quad $(addition: associative property)
$=25+2x\quad $(combining like terms, simplification of parentheses)
$=2x+25\quad $(addition: commutative property)

#### Work Step by Step

Commutative properties: $a+b=b+a,\qquad ab=ba$
Associative properties:$ a+(b+c)=(a+b)+c,\qquad a(bc)=(ab)c$
Distributive property: $\quad A(x+y)=Ax+Ay$
Combine like terms by combining the coefficients of the terms and keeping the same variable factor.
---
$7+2(x+9)$
$=7+(2x+18)\quad $(distributive property)
$=7+(18+2x)\quad $(addition: commutative property)
$=(7+18)+2x\quad $(addition: associative property)
$=25+2x\quad $(combining like terms, simplification of parentheses)
$=2x+25\quad $(addition: commutative property)