A sample of propane c3 h8 contains 10.0 miles of carbon atoms

We need to calculate the ratio of C to H in the molecule:

We have 3 C and 8 H, so the ratio is 3:8

If we have 10.0 moles C, we divide that by the number of C atoms to get the factor:

10/3 = 3.33

The we multiply the number of H atoms, 8, by this factor:

3.33 x 8 = 26.67

So we have 10.0 moles of C and 26.67 moles of H for a total of 36.67 moles in the sample.