The answer is: a = 16
Steps:
First exclude any restricted values of y. 
6/y = 9/24 , y is not equal 0
Simplify the right side of the equation using 3. 
6y = 3/8
Cross multiply. 
6 x 8 = 3
3 x y = 3y
So, 6 x 8 = 3y
Or, 48 = 3y
Switch the sides of the equation. 
3y = 48
Divide both sides by 3. 
3y/3 = y
48/3 = 16
Now you have your answer, y = 16