Question

At a restaurant the ratio of kids meals sold to adult meals sold was 3:9. If there 12 kids meals sold, what is the combined amount of kids and adult meals sold?

Answer 1

$\frac{3}{9} = \frac{12}{x} 3x = 108, x = 36 36+12 = 48$

Answer 2

Have the unknown amount = x 
so 3x : 9x
 you know how many kids meals were bought is equal to the ratio (3x = 12, so x=4)
you already know how many X's for the adults (9) so just multiply (9x4= 36)
lastly add since you need to find the total meals bought (36+12= 48)