I. v r v . v m 3- j 9- i 9-3 war i . a v next . 1 new . i n r . a. m lyn ff v . .

We have an arithmetic progression:
an=a₁+(n-1)d
an=Nth term
a₁=first number of the serie
n=Total number of terms in the serie.
d=difference between two successive numbers

a₁=37
d=a₂-a₁=30-37=-7

therefore:
an=37+(n-1)(-7)
an=37-7n+7
an=44-7n

  an= 44 -7n

To check:

if n=1; ⇒a₁=44-7*1=37
if n=2; ⇒a₂=44-7*2=30
if n=3; ⇒a₃=44-7*3=23