The number of moles of hydrogen produced will mirror the number of moles of Zn that react, or, from a different perspective, will be half the number of moles of HCl that react.
The balanced chemical equation for this reaction is
Zn_((s)) + 2HCl_((aq)) -> ZnCl_(2(aq)) + H_(2(g))
Now look at the mole ratios you have between Zn, HCl, and H_2: 1 mole of Zn needs 2 moles of HCl to produce 1 mole of H_2.
All you have to do now is figure out exactly how many moles you have. This is done by using the molarity of the HCl solution to calculate how many moles of HCl you have, since you know that Zn is in excess.
C = n/V => n_("HCl") = C * V = "0.40 M" * 400*10^(-3)"L" = "0.160 moles"
Therefore, the number of H_2 moles will be
"0.160 moles HCl" * ("1 mole H"_2)/("2 moles HCl") = "0.800 moles" H_2
