98.3, 94.1, 89.9, 85.7 ... is what sequence

Hmm, it might be aritmetic

so

89.3-94.1=4.2

94.1-89.9=4.2

so it is an aritmetic sequence with common differnce of - 4.2

an=a1+d (n-1)

a1=first term

d=common differnce

n=which term

an=nth tem

so

the equation is

an=98.3-4.2 (n-1) or

an=102.5-4.2n

If you mean Arithmetic or Geometric it is: I believe it is Arithmetic.