A series is given with one term missing. Select the correct alternative from the given ones that will complete the series. YEW10, ?, WAQ22.5, VYN33.75, UWK50.625

First letters decrease by 1 (Y,X,W,V,U), second letters decrease by 2 (E,C,A,Y,W), third letters decrease by 3 (W,T,Q,N,K), numbers: 10×1.5=15, 15×1.5=22.5, 22.5×1.5=33.75, 33.75×1.5=50.625. The missing term is XCT15.