Answer:
4/13
Step-by-step explanation:
We can first find the GCD or GCF of 28 and 91. 91 in its simplest form is 13*7. 28 in its simplest form is 2*2*7. The only common factor they have is 7, so 7 is the GCD. We can divide both by 7 to get [tex]\frac{4}{13}[/tex]
