Question 637879
To solve, substitute 3 for a:

(6-8*3)/(6*3+9)

Using the order of operations, we would first simplify each set of parenthesis:

(6-24)/(18+9)=-18/27

Since 9 is a factor of both the numerator and demominator, we can divide both the numerator and denominator by 9 to reduce the fraction to lowest terms.  Therefore,

-18/27 = -2/3

Answer: -2/3