Assuming the values following t are subscripts since this is a sequence:
The +4 tells that the Common difference of each term following the previous one is 4. You could keep adding by doing
t2=t1 + 4 t2=2+4 = 6
t3=t3 + 4 t3=6+4 = 10
.....and so on.
Or you could turn the recursive rule
tn=t(n-1) + 4 into an explicit rule.
tn = t1 + 4(n-1)
So, tn = 2 + 4(n-1)
where n is the term number.
To the sixth term, make n=6 and solve.
t(6) = 2 + 4(6-1)
t(6) = 2 + 4(5)
t(6) = 2 + 20
t(6) = 22
So the sixth term in this sequence is 22.
