if you multiply both fractions by their LCD, namely 72, you'll in effect be removing the denominators, and you can see how is larger then,
[tex]\bf 72\cdot \cfrac{7}{9}\implies \boxed{56}\qquad\qquad \qquad 72\cdot \cfrac{5}{8}\implies \boxed{45}[/tex]
surely you'd know what's larger, 56 or 45.
now, the fractional way to do it is, "you multiply top and bottom of each fraction by the other's denominator", so let's do it that way,
[tex]\bf \cfrac{7\cdot 8}{9\cdot 8}\implies \boxed{\cfrac{56}{72}}\qquad \qquad \qquad \cfrac{5\cdot 9}{8\cdot 9}\implies \boxed{\cfrac{45}{72}}[/tex]
that way they both will have the same denominator, and surely you can see who is larger.
