What is ec if ac = 12, bc = 5, and dc = 4? a. 30 b. 9 c. 15 d. 7

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

The number of students that brought in can are 20