The answer is wrong, the correct answer should be 5.

P_(total) = 6 atm
Molar mass of He = 4g/mol
Molar mass of Ne = 20g/mol
so their molar masses are in the ratio of 1 (He): 5 (Ne)
so is masses are equal ,it means moles are in the ratio of 5(He):1 (Ne)
Partial pressure of He = X _(He) *P_(total)
X _(He) is the mole fraction of He = 5/6
Partial pressure of He =5/6*6  = 1 atm
You are correct !