1. Use Un formula
The 10th term = 5 + (10-1) x 8
= 5 + 9 x 8
= 5 + 72
= 77
The 20th term = 5 + (20-1) x 8
= 5 + 19 x 8
= 5 + 152
= 157
The 50th term = 5 + (50-1) x 8
= 5 + 49 x 8
= 5 + 392
= 397
2. 4.
The 4th term = 39
Term-to-term rule is add 7.
1st term is …?