225 cm³ of hydrogen at S.T.P is heated such that its pressure is 810 mm of mercury at a temperature of 97 ^oC. Find the volume of gas

At STP 22400 mL is occupied by 1 mole of a gas
Therefore, number of moles of hydrogen gas in 225 ml ( 225 cm³) = (1/22400) $\times$ 225
  = 0.01
Now,
760 mm Hg = 1 atm
810 mm Hg = 1.065 atm
97 degree Celsius = 273 + 97 = 370 K

Applying,
PV = nRT
V = (0.01 $\times$ 0.0821$\times$ 370) / 1.065
  = 0.2852 L
  = 285.2 mL