1 shoe = 5
1 boy = 5
1 unknown thing = 2

1. 6 (5)shoes = 30
2. 2 boys (5) + 2 shoes (5)= 20
3. unknown thing 4 (2) + boy (5) = 13
4. shoe (5) + boy (5) + 2 unknown things (2) + 2 shoes (5) x unknown thing (2)

--> 5 + (5+4+10) x 2
--> 5 + 19 x 2
--> 5 + 38
--> 43