Avagadro's law gives the relationship between volume of gas and amount of moles of gas. It states that at constant temperature and pressure, volume of gas (V) is directly proportional to number of moles of gas (n).
V/n = k
where k - constant

V1 = 42.0 L
n1 = 1.90 mol
n2 = 1.90 mol - 0.600 = 1.30 mol
substituting the values in the equation

V = 28.7 L
Volume of the gas is 28.7 L