we need to find ED first
the formula for this would be (AB +BC)*BC = (ED+DC)*DC
lets replace the letters with the given numbers:
If AC = 12 and BC = 5 then AB = 12-5 = 7
so we get:
(7+5) *5 = (ED+4)*4
12*5 = (ED+4)*4
60 = (ED+4)*4
60/4 = (ED+4)
15 = ED +4
ED = 15-4 = 11
now add ED + DC to get EC
11+4 = 15
The answer is C. 15
