No Sweat! Put the 1 and the 5 in the second box and 15 in the third box: 15 + 15 equals 30. It doesn’t say you have to fill all the boxes, and it doesn’t say you can’t put more than 1 number in a box. It does say you can arrange them how you like, and you do have to use 3 of them. Having to use all three boxes is an unwarranted assumption.