You cant simplify it . it is already simplified
Basically think of linear functions/equations as something with a constant value or consistent result. For example: (Attachment)
Doubling the side length multiplies the area by 4
48 = 2*2*2*2*3
84 = 2*2*3*7
Looking for common factors we get the GCF to be 2*2*3 = 12
Its B