The question is asking we convert from (x, y) coordinate to (r, theta) coordinates.
So (0, 4) to (r, theta)
x = 0 and y = 4.
r = âš (x^2 + y^2)
r = âš (0^2 + 4^2)
r = âš (0 + 16)
r = 4
Also theta = tan^(-1)(x/y) = tan^(-1) (0/4) = 0
So theta = 0
Hence the (r, theta) coordinate is (4, 0)