Molly is designing a new drone for the air force. the drone is supposed to be 30 feet long and 4 feet tall. she is building a prototype for testing that will be 12 feet long. how tall should the prototype be?

First you set up your ratio: Length to height.
The Drone is 30/4 which can be equivalent to 7.5.
The prototype is 12/x which can be equivalent to 7.5 as well. Re-write your equation to solve for x.
x*7.5 = 12 ---> x=12/7.5. =  1.6. Now plug in 1.6 as x to test your equation so you get an answer of 7.5: 12/1.6 = 7.5. 
So, the prototype for testing should be 12 feet long and 1.6 feet (19.2 inches) high.