we have that
-3r+3u
Step 1
Use the distance formula to find the radius
r = √(x^2 + y^2)
(x,y)----------> (-3,3)
r= √(-3^2 + 3^2)=√18=3√2
Step 2
Use the tangent to find the angle
θ = arctan(y/x)
θ = arcTan(3/-3)= -45°-------> II Quadrant
then
θ=180-45=135°
Step 3
write in polar form
(x,y)------------> (r, θ)
so
(-3,3)----------> (3√2, 135°)
the answer is (3√2, 135°)