interpolating on logarithmic graphs

Hi everyone,

I am taking Properties of Materials, however, there is a question that involves some applied algebra.

Here is my problem: I am shown a graph of a line with a positive slope, however, the abscissa is in logarithmic scale. Even though the graph appears to be linear, it says the function is NOT linear. It wants me to interpolate data, but using y = mx + b does not give me consistent answers (even though I have what appears to be a y-intercept and linear-looking line). How can I interpolate data on logarithmic scales? I believe this would be considered a semi-logarithmic plot.

Thank you!