The valve between a 5 liter tank in which the gas pressure is 911.925 kPa and a 10 liter tank containing gas at 4560 torr is turned open and equilibrium is established at constant temperature. What is the final pressure in the two tanks in atmospheres?

I would use PV = nRT to solve for n in tank 1, use PV = nRT to solve for n in tank 2. Then total moles = n1 + n2 and use the sum to calculate P in the two tanks. Use PV = nRT where V is total volume, n is total moles.