## Calculus with Applications (10th Edition)

$-\displaystyle \frac{6}{11}$
The aim is, step by step, to isolate $a$ on one side of the equation. ...Multiply out the parentheses $5a+15+4a-5=-2a+4$ $...$add/subtract like terms on the left side $9a+10=-2a+4$ ...Subtracting 10 from both sides removes it from the left side ...Adding 2a to both sides removes it from the right side $9a+10=-2a+4\qquad.../-10+2a$ $9a+2a=4-10\qquad ...$simplify $11a=-6$ ...Dividing both sides with $11$ isolates $a$ on the left side. $a=-\displaystyle \frac{6}{11}$