Question

which term of the series 3,8,13,18,23.........is 78?

Answer 1

a=3
d=5
Tn=78
n=?

Tn=a+(n-1)d
78=3+(n-1)5
78=3+5n-5
78=5n-2
78+2=5n
80=5n
n=80/5
n=16

Answer 2

The next terms 28 ,33,38,43,48,53,58,63,68,73 and 78.There is plus5 on each term.
Hope it will help you.