You have an unknown quantity of oxygen at a pressure of 2.2 atam, a volume of 21 liters and a temperature of 87 celsius. how many miles of gas are left for you to breath

Let's assume that the oxygen gas has ideal gas behavior. 
Then we can use ideal gas formula,
      PV = nRT

Where, P is the pressure of the gas (Pa), V is the volume of the gas (m³), n is the number of moles of gas (mol), R is the universal gas constant ( 8.314 J mol⁻¹ K⁻¹) and T is temperature in Kelvin.

P = 2.2 atm = 222915 Pa
V = 21 L = 21 x 10⁻³ m³

n = ?

R = 8.314 J mol⁻¹ K⁻¹

T = 87 °C = 360 K

By substitution,
222915 Pa x 21 x 10⁻³ m³ = n x 8.314 J mol⁻¹ K⁻¹ x 360 K
                                       n = 1.56 mol

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i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)