Whats the answer for this
4b²+20b+25

4b²+20b+25=0

Divide everything by 4 

b²+5b+ 6.25=0 

use the quadratic formula 
x= (-b+ or - √b²-4ac) /2a
x= (-5 + or - √5²-4*1*6.25) /2(1)
x= -5/2 so
in this case, b= -5/2

If the diameter is 8 than the radius is 4 because 2r or 2*radius equals the diameter. 4*2=8. 8/2=4.