Please help me with the question below

15 feet

Explanation:
Triangle ABC is similar to triangle EDC, meaning they would’ve been congruent if it weren’t for their size.
This also means they don’t have the same side lengths but have the same proportions in comparison to each other.

The sides on the two triangles also correspond with each other. For example, line DC corresponds with line BC.
Knowing that, we can conclude that line ED also corresponds with line AB. Line ED is 12 ft and line AB is 4 ft. To get from 4 to 12, you multiply 3 (4*3=12).

Line EC also corresponds to line AC. So to calculate for line EC, we multiply the length of line AC by 3. 5*3=15, so therefore line EC is equal to 15.