The expected answers were:
(a) Reactance is the opposition afforded by a pure inductor or pure capacitor to the passage of alternating current.
(b)(i)  The inductive reactance,

XL = 2pfL
XL  =  2p  50 x 15 x 10-3
 XL  =  4.71Ω
 (ii)   The phase angle θ = tan-1 wL/R  =  tan-1 XL/R  = cos-1 R/Z 

=  tan^-1 4.712 / 20 

θ  = 13.26o

This question was on alternating current circuit theory.  This was well attempted by many candidates.  Many candidates got the definition, computed correctly but got the phase-angle wrong because they could not relate it to the impedance triangle.