The STP as specified by the IUPAC is a temperature of 273.15 K and a pressure of 100 kPa.
Now we use the Ideal Gas Law, PV= nRT, where P denotes pressure, V denotes volume, n is the amount of the gas in moles, R is the universal gas constant and T is the temperature.
We have collected 1.85L of a gas at 97.0 kPa and 28 degree Celsius or 28+ 273.15 = 301.15 K
So we can take V1 = 1.85L, P1 = 97 kPa and T1= 301.15.
From the Ideal Gas LAw, n = P1*V1 / R*T1 = P2*V2 / R*T2
P2 which is the pressure at STP is 100 kPa and T2 at STP is 273.15K. We need to find the volume V2. An the number of moles n is the same we get the relation:
P1*V1 / R*T1 = P2*V2 / R*T2
=> 97* 1.85/ R*301.15 = 100*V2 / R*273.15
=> V2 = 97* 1.85*R*273.15 / R*301.15*100
=> V2 = 97* 1.85*273.15 / 301.15*100
=> V2 = 1.6276
Therefore the volume at STP is approximately 1.6275L