63
87-63 = 24
It is 87, the number halfway between the two middle numbers.
24 plus 63 is equal to 87.
The halfway point is on I-87, just north of the NJ/NY state line, near Tuxedo Park, NY.
65
1827
87 - 39 = 48
57
69.7241
88 and 88.1, for example.
The GCF is 3.