Shouldn't be too difficult, but won't be 100% accurate either
Regarding difficulty, just an exercise in careful work. The number crunching is pretty trivial.
Accuracy should be exact to the limit of your ability to read off chart data .. suggest you scan at a reasonably high res and zoom in to read data points.
Again, this is a standard weight control engineering exercise so, should you find yourself in any difficulty, we can assist as you might require.