Using the quadratic formula i can't remember what to do next

you square root it.

5r^2/5 = 80/5 =16

Sqr root of r^2=Sqr root of 16

r=4

Step-by-step explanation:

Well first the answer is wrong. But In order for 10.36 +7.6+7.6 (which equals 25.55) then K has to be 17.95. 
So how this problem should've been solved is:
K - 7.6 = (10.35 + 7.6 + 7.6 = 25.55) 
25.55 - 7.6 = 17.95
So the error Noam had was in the answer for K which is 17.95 not 17.41