Two sides of a triangle are marked as 10 and 7 units long. Write a whole number length that could work as the length of the 3rd side in the triangle.

18

Step-by-step explanation:

it is a fundamental principle that sum of any two sides must be greater than third side

since sum of given sides is 10+7 = 17

hence any number greater than 17 for example 18 can be third side but confirm it with other sides

18 + 10 is greater than 7 also 18+7 is greater than 10

hence other side can be 18