but i thought the "per 100,000 " means that we get for example 5 cases out of 100,000 1970 .. amerite? which makes it 5-1.75 / 30 which is closest to 0.13?

I thought E is the correct answer.

.13

Great point!
In my haste, I misread the vertical scale as telling us the NUMBER of cases (in hundred thousands).

Since we don't know the total population, there's no way to determine the average yearly increase in the NUMBER of incidences of melanoma.

For example, if the total population = 100,000, then that means there were 1.2 incidents in 1940, and there were 5 incidents in 1970. This means the average annual increase = (5 - 1.2)/30 = 0.13 per year.

Conversely, if the total population = 1,000,000, then that means there were 12 incidents in 1940, and there were 50 incidents in 1970. This means the average annual increase = (50 - 12)/30 = 1.3 per year.

For this reason, this is a faulty question.