We know that the lengths of the two smaller sides have to be more than the third side when they are added together
The third side couldn't be 2 or 3 because 9 (7+2) or 10 (7+3) are not less than 10
The third side couldn't be 17 or 18 because 17 (7+10) is not larger than 17 or 18
The correct answer is C. 4 works because 7+4=11 or more than 10. 16 works because 7+10=17 is more than 16
Hope this helps
