Three tickets cost $7 x 3 = $<<7*3=21>>21.
Two boxes of popcorn cost $1.5 x 2 = $<<1.5*2=3>>3.
Three cups of milk tea cost $3 x 3 = $<<3*3=9>>9.
The total expenses for the their tickets and food are $21 + $3 + $9 = $<<21+3+9=33>>33.
So, each of them should contribute $33/3 = $<<33/3=11>>11.
#### 11