The problems:

0.0513 grams of Al (Wt. 27.0) was reacted with excess HCI to produce H2 according to the following balanced equation:

2 Al + 6 HCI ---> 2 AlCl3 + 3 H2

a) Determine the number of moles of H2 evolved from that quantity of Al when collected over water?

0.0513g Al x 1 mol Al / 27g Al x 3 mol H2 / 2 Mol Al = 0.00285 mol H2

b) If the volume of gas generated was 75mL and the temp was 27°C , determine the total pressure of the hydrogen gas evolved from the quantity of Al stated above?

PV=nRT --> P = nRT/V

(0.00285)(0.082)(300) / 0.075 = 0.9348

c) The vapor pressure of water at 27°C was 26.7 mmHg, determine the partial pressure of the hydrogen gas collected in mmHg?

And this one I cant find an example in my book so I don't know which formula to follow.