Write the fraction below in simplest form.
Since you might not be able to see asinus's answer, (as it is written in raw LaTeX, probably another glitch), let me help write it out in pure letter and number form. We see that both 12 and 5 share a 6. So divide both by 6, and we see that the coefficient is 2/5. The only two that satisfies that is A and B. We see that 1 of the a's cancel out, which leaves us with a squared. Therefore, the only possible answer is A.
if you want a more 'mathematical' answer, check out asinus's post (which is also great!). Maybe you are smart enough to crack Tex code!