#### Answer

$a=4$

#### Work Step by Step

We start with the given equation: $5a-15+9a=3a+29$
We add $15$ and subtract $3a$ from both sides of the equation: $5a-15+9a+15-3a=3a-3a+29+15$
We combine like terms on both sides of the equation: $11a=44$
Finally, we divide by $11$ on both sides of the equation: $a=4$