Soccer ball represents 6:
6 + 6 + 6 = 18
18 is a composite number that factors into 1, 2, 3, 6, 9 and 18. We can divide 18 by 3 to get 6 for repeated subtraction: 18 - 6 - 6 - 6 = 0.
Clock represents 3:
3 + 3 + 3 = 9
9 factors into 1, 3 and 9. Again, there are three in the group so 9 / 3 is 9 - 3 - 3 - 3 = 0.
Plant represents 4:
4 x 4 - 4 = 12
x squared minus x: x(x-1) = 12
4(4-1) = 12
Therefore, Clock x Soccer ball - Plant represents:
3 x 6 - 4 = 14
? = 14