I will assume that you mean #"STP (Standard Temperature and Pressure)"#.
Since we know that #"1 mole"# of an ideal gas occupies #"22.4 L"# at #"STP"#, then can establish the following relationships:
#color(white)(------)color(orange)[("22.4 L")/("1 mole") or ("1 mole")/("22.4 L")#
Knowing that, we can solve for the volume occupied by the helium gas,
#(0.35 cancel"mole")/(1) * ("22.4 L")/(1 cancel"mole") = color(blue)"7.84 L"#
as #color(blue)"7.84 L"#
#--------------------#
The answer makes sense because if #"1 mole"# occupies #"22.4 L"#, then #"0.35 moles"# (roughly a third of the moles) will occupy a third of #"22.4 L" ("if we round down 22.4 L to 21 L")#
#color(white)(--------)21/3 ~~"7 L"#
