you just have to substitute x into the equation, so when it says x is 1, you substitute 1 into the equation given, in this case it's y = 26 - 4x. After that, you just do regular math to get your y value
Since (density = mass/volume), we can get the mass/weight of the liquid by integrating the density over the interior of the tank. This is done with the integral
which is more readily computed in cylindrical coordinates as
