The solubility of helium is ##5.6 × 10^(-4) “mol·L”^(-1)##.
Henry’s Law is often written as
##C = kP##,
where ##C## is the concentration of the gas in the solution, ##P## is the of the gas, and ##k## is a proportionality constant.
For your problem,
##C = kP = 3.70 × 10^(-4) “mol·L”^(-1)color(red)(cancel(color(black)(“atm”^(-1)))) × 1.5 color(red)(cancel(color(black)(“atm”))) = 5.6 × 10^(-4) “mol·L”^(-1)##.



