A level book question. Please solve for me

(a) Assuming air to be an ideal gas, calculate the number of moles of air left in a scuba diver's tank if it has a volume of
12 litres and, when in 15 C° water, the pressure is 2× 10^7 Pa.
(b) What would be the new rms speed of the molecules in the scuba tank when it is immersed in water so its temperature becomes 12°C?

the answer to the first question is 100.3 mol.
but i cant calculate the answer to the second one..........

You can use
$v_{rms} = \sqrt{\dfrac{3RT}{M}}$
where M is the molar mass in kilograms per mole.