The formula for this is

. Filling in accordingly,

. This simplifies to

and 36=6x. Therefore, x = 6 so the bases are 6 and 12.
Solution
For this case we can do the following:
11y - 3x = 18
16y -3x = 33
We can multiply the first equation by -1 and we got:
-11y +3x =-18
16y -3x = 33
_______________
16y -11y = 33-18
5y = 15
y= 15/5 = 3
And then solving for x we got
x = -(18 -11*3)/ 3= -15/3 = 5
The answer is e, 3 3/4
if you add 3/4+3/4+3/4+3/4+3/4 (five times for the five batches), or did 3/4 * 5, you would get 15/4, which simplifies to 3.75, or 3 3/4
Does this help you at all?