Hey there!
We see that 90 hazel nuts have a mass of 125 g. First, let's find the ratio of hazelnuts to calories. First, we will want to get down to 100 grams of hazelnuts.

We cross multiply and solve for h.
125h=9000
We divide both sides by 125.
h=72
Therefore, 72 hazelnuts have 630 calories. We can plug this into a new proportion and see how many calories one hazelnut has.

We cross multiply and solve for c.
72c=630
We divide both sides by 72.
c= 8.75
Therefore, one hazelnut contains 8.75 calories.
I hope this helps!