we have that
In this problem we have an arithmetic sequence
the general equation is equal to
an=a1+D(n-1)
where
a1 is the first term
D is the common difference
n is the number of terms
so
a1=7
D is the difference between consecutive terms
D=11-7=4
an=7+4(n-1)
change the variables
d=7+4(n-1)
d=7+4n-4
d=4n+3
For n=30
d=4(30)+3
d=123