Answer:
2 < c < 12
Explanation:
If we know two sides of a triangle a and b, the third side, c, can be no bigger than the the other two sides added together, and no smaller than the other two sides subtracted
a-b < c < a+b
We know the two sides are 7 and 5
7-5 < c < 7+5
2 < c < 12