9. Two plates are diverging and both are moving at a rate of 3 cm per year. How long will it take for them to move 100 km apart?

Question

I am getting confused about this question, as i looked at a few ways got different answer but not 100% which is the right answer?

Answer 1

3 cm per year would be 3 m per 100 years.

 

Then 100 km is 10⁵ m, so use a proportion:

 

3 m / 100 yrs = 10⁵ m / t years.

 

I let you solve for t in this proportion.