Before a trip from new york to boston, the pressure in an automobile tire is 1.8 atm at 20.°c. at the end of the trip, the pressure gauge reads 1.9 atm. what is the new celsius temperature of the air inside the tire? (assume tires with constant volume.) answers

Gay-Lussac's law gives the relationship between pressure of gas and temperature. It states for a fixed amount of gas, the pressure of gas is directly proportional to temperature at constant volume. 
P / T = k 
where P - pressure, T - temperature in Kelvin and k - constant

where parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation
T1 - temperature in Kelvin - 20 °C + 273 = 293 K
substituting the values in the equation 

T = 309 K 
new temperature in celcius scale - 309 K - 273 = 36 °C