Answer: 3.5m
Explanation:
We can set up a proportion to help us solve this question. The triangle with side lengths of 4m, 4m, and 2,m is similar (proportional) to the triangle with side lengths of (4m + 3m), (4m + 3m), and ?m.
Given:

Addition:

Cross-multiply:
4m * ? = 2m * 7m
?4m = 14m
Divide both sides of the equation by 4:
? = 3.5m