Boyle's law describes the relationship between pressure and volume when temperature is fixed; Charles' law relates volume and temperature when the pressure is constant. We can combine these two laws into the ideal gas law-ideal because it is obeyed strictly by no real gases, but is followed more and more closely as the pressure decreases and temperature increases. For n moles of an ideal gas
PV = nRT
The gas constant, R, is a fixed quantity, independent of pressure,

volume, temperature, or amount of gas.
If pressure is measured in atmospheres, volume in liters, and temperature in degrees Kelvin, then R has the numerical value
R = 0.0821 liter deg

The ideal gas law is much more powerful than either Boyle's or Charles' laws alone. We now can calculate how many moles of hydrogen gas there were in the weather-balloon example, assuming a temperature of 25.