"what is the pressure of a 34.8-l gas sample containing 7.45 mol of gas at 19.9°c? (r = 0.0821 l • atm/(k • mol), 1 atm = 760 torr)"

You can solve this problem using ideal gas formula (PV=nRT). Remember that the temperature used is Kelvin, so 19.9°c would be: 19.9+ 273.15= 293.05°K

PV=nRT
P= nRT / V
P= 7.45 * 0.0821* 293.05 / 34.8
P= 5.15 atm = 3914.5 torr