Que es mayor tres cuartos o tres octavos

Lets do compare both fractions, and suppose the first is greater:
3/4 > 3/8
to ease the comparison, we change the first fraction to eights:
3/4 = 6/8, lets use this:
3/4 > 3/8
6/8 > 3/8

So we can see that the left fraction, 6/8 = 3/4 is greater

Ac equals 35 cm long