Answer
The statement is true.
Work Step by Step
$7a+(4+5a)=7a+(5a+4) \qquad $(commutative property of addition)
$=(7a+5a)+4\qquad $(associative property of addition)
$=(7+5)a+4\qquad $(distributive property of addition)
$=12a+4\qquad $(simplify 7+5)
(LHS = RHS)
The statement is true.