Compare an Array to a Array in an Array

I Wish to Compare array A with Array C but Array C is inside of Array B.

I have tried doing something like this but the results vary:

a.forEach(var => {
 if(var.C.includes(A)){
 //Do Something
 }
});

Minor Idea of what the Arrays look like:

A = day: "10"; 

B= {
someRandom: "Something",

C: [{
 day: "15"
}]
}