Method 1:
Sabrina: 4/13 (Fraction... you can just turn them into fractions)
Garrett: 2/7
Matthew: 3/8
LCM (The number that all three denominators multiply into) is 728
S: 4/13 x 728 = 224
G: 2/7 x 728 = 208
M: 3/8 x 728 = 273
Now you can rank those numbers from greatest to least.
Method 2:
Sabrina: 4/13 (Use fractions again)
Garrett: 2/7
Matthew: 3/8
Now actually solve the fractions... (calculator recommended.)
S: 4/13 = 0.30
G: 2/7 = 0.28
M: 3/8 = 0.37
You can list those in order too.
Hope this helps!
-A