the underlying formula that you want to use to convert these over are
r = +/- sqrt(x^2 + y^2)
tan(theta) = y / x
for this set of parameters that means taking
r = sqrt(4(sqrt(3)^2) + 4^2)
r = +/- 8
tan(theta) = y/x = 1/sqrt(3)
theta = 30 +/- pi
then based on the other constraints it would be
(-8, 7pi/6) since we need r to be negative