We let x be the common number in which we can multiply the ratio 2:1 to obtain the desired volume, 180. If we add 2x and 1x (or simply x), the answer should be 180.
2x + x = 180
The value of x from the generated equation above is 60. Therefore, the amounts of Maalox and Donnatal are equal to 120 and 60 mL, respectively.
