Samantha is 1.1 m tall on her eleventh birthday and 1.21 m tall on her twelfth birthday. by what factor has her height increased?

Well to figure this out you can simply get how tall she is now which is 1.21 m tall and subtract how tall she used to be which is 1.1 from that. 
If you subtract them you should have got 0.11 m making the total that she grew to be 0.11. 
Hope I Helped.:)

It should be d if not then c