Do you know what the "vector diagram" is? (Someone shall correct me, if my english is wrong!)
The vector diagram shows the Û- and the Î-vector rotating counter clock wise. The angle between the two vectors represents the phase shift of Û relative to Î.
You can also draw the Z-vector in this diagram: Z is the quotient of Û and Î, where Û and Î means the amplitudes of U(t) and I(t), represented by the lengths of vectors. Z is the complex impedance of the circuit of course.
You can also draw the Z-vector, as follows: Chose a length that is equal to Û/Î and draw it under an angle to the real-axis which is equal to the phase shift of Û relative to Î. So, if the phase angle between Û and Î is zero, then the Z-vector will coincide with the real-axis.
The projection of Z-vector onto the real-axis will give you "R" and the projection of Z-vector onto the imaginary-axis will give you "X"!

How can you deduce Z from the "R"- and "X"-plots from the picture of your exercise then?

What must Z be at very low and very high frequencies?

What kind of circuit can you clearly deduce from that?

Kai