The formula to the solution is as follows:
x = amount spent per person
d = drink
p = popcorn and
vc = veggie cup
this makes
(p+vc)/2 = they shared the poppcorn and the veggie cup and thus the sum musst be divided by the amount of sharing people which is two.
=> x = d + (p+vc)/2
And since there is no money mentioned for the movies (m) it is teh formula above.
If you would like to consider that costs too it would be:
x = m + d + (p+vc)/2
