Hi Karsang,

The transition from n=2 to n=1 will have the same wavelength. You can check it using the formula to calculate wavelength. 1/(wavelength) = R * Z^2((1/n1^2)-(1/n2^2)).

R is a constant. Z is 2 for He and 1 for H. put values of n1 and n2. and equate both wavelengths. You'll get answer  n1=1. n2 = 2, for hydrogen.

Feel free to message for doubts.