Which transition in Li2+ would have the same wavelength as the 2 → 4 transition in He+  ion?

ν¯=1λ=RZ21n12-1n22  ν ¯2→4He+ =1λ = R(2)214-116=34R= ν ¯x→yLi+2 (If λ is same then ν is also same)  3R4=R(3)21x2-1y2  from options , x=3 , y=6