a level biology maths question

heyy how do i do this?

Oh it’s a logarithmic scale (bleurgh)
Essentially, despite not being evenly spaced, any consecutive divisions between 10 and 100 are separated by 10, any consecutive divisions between 100 and 1000 are separated by 100 and any consecutive divisions between 1000 and 10000 are separated by 1000.
The cell growth is equal to the control when the proportion is 1.0 (which corresponds to concentrations in the range 30 - 70 μg dm^-3) and is 0.0 at 2000 μg dm^-3.
You should be aware (from GCSE / A level chemistry) that concentration = mass/volume, so mass = concentration x volume.
Since 0.01 dm^3 of solution is used and we know some relevant concentrations, we can deduce that:
0.01 dm^3 x 2000 μg dm^-3 = 20 μg when the proportion is 0.0
0.01 dm^3 x 30 μg dm^-3 = 0.3 μg OR 0.01 dm^3 x 70 μg dm^-3 = 0.7 μg when the proportion is 1.0
Calculating the difference gives you either 19.3 μg or 19.7 μg
Imo this question would have been much easier if they didn’t require you to understand logarithmic scales and it’s an unnecessary amount of work required for just two marks.