For what value of c will the circle with equation x^2 + 6x + y^2 - y + c = 0 have a radius of length 4?
Complete the square for x and y to get tstandard circle form equation
(x+3)^2 + (y - 1/2)^2 = 9 + 1/4 - c
9 + 1/4 - c must equal r^2 = 16
c = - 6.75