Multiply [tex] \frac{3}{4} [/tex] by 2 to get a common denominator.
That'll then show you that [tex] \frac{3}{4} [/tex] is bigger, as:
[tex] \frac{3}{4} [/tex] × 2 = [tex] \frac{6}{8} [/tex]
and,
[tex] \frac{6}{8} [/tex] is bigger than [tex] \frac{3}{8} [/tex]