From evaluating the integral with respect to x between the limits 0 and 3. so having evaluated that, you can now go on to do the integrals in y and z.
Sorry if ive put this in the wrong category again, i dont know where this belongs, in uni my lecteur puts this under calculus.
Gas is contained in a box defined so that it extends in each axis from 0 to 3.
The density of the gas is given by the formula
Ive no idea where the two 9's come from in the next line, could anyone explain this