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In 2004 astronomers reported finding evidence that certain white dwarfs are 12.1 +- 0.9 billion years old. Assuming an inflationary model in which the age of the universe is approximately equal to Hubble time, what limit does this measurement set on the possible values of Hubble constant H-0?

My work: if the age of the universe is equal to Hubble time, and Hubble time is equal to 1 over the Hubble constant, than wouldn't the limit of the age of the universe be 13 bya, thus 13bya = 1/H-0, and 11.2bya = 1/H-0, making the answer and the limit on the Hubble constant to be a value in between 1/13bya and 1/11.2bya? How would I make this information into a answer for that question?

In March 2004, astronomers reported measuring a record redshift for a galaxy. z=10. Assuming that this redshift is due to the expansion of the universe, what is the ratio of the scale factor of the universe when the light was emitted to its scale factor now? (In other words, find R-then / R-now where R is the scale factor of the universe)

I have no idea how to start this one.

Any steps in the right direction or links with these types of problems and their solutions would be much appreciated. Thank you.