Interperating a graph with logarithmic scales

1. The problem statement, all variables and given/known data
see attachment


2. Relevant equations
log₁₀x=y
10^y=x


3. The attempt at a solution
Since I'm rather confused on reading a logarithmic scale, I thought I'd post this to see if I'm doing this right and/or if there's a better way to do the problem.

a) T=500 C
using the # of intervals we can say that if d=.01, x=.5 intervals so...
log(t)=.5
t=3.16 min

similarly for d=.1
log(t)=3.5 intervals
t=3162

change in time = 3162-3.16 = 3158.8min

b) same process but use x=-.5 intervals and x=2.1

If this method does work, is there any way to interpolate values so I can be more exact? or is there a better way to do the problem in general?
thanks!

 

yah, I was worried about being able to get a precise enough answer to matter. I think later I'll find a ruler and figure out more exact data points
thanks!