Problem Solving

hi,
i know how to solve this problem through backsolving, but i'm not sure how to solve it through setting up an equation...any suggestions would be great

Four cups of milk are to be poured into a 2 cup bottle and a 4 cup bottle. If each bottle is to be filled to the same fraction of its capacity, how many cups of milk should be poured into the 4 cup bottle?

A 2/3
B 7/3
C 5/2
D. 8/3
E 3

Thanks, guys!!

we know that the two cups need to be filled to the same fraction

let x be the amount of milk being put into the 4 cup bottle.

x/4 = (4-x)/2
2x = 16-4x
6x =16
x = 16/6 = 8/3

So, D.

Can't you just figure it out by knowing you have to fill a total of 6 cups with only 4 Cups worth of liquid? So that would be 4/6 or 2/3.

2/3 of the 4 Cup Bottle = 8/3

I could be wrong but that would be my approach