I'm so sorry if this was confusing for you but just saying the answer clearly is (4,24)
I believe the answer is b
The 1st term is 60.
Add 50 to this to get the 2nd term, 60 + 50 = 110.
Add 50 to that to get the 3rd term, 110 + 50 = 160.
Add 50 to that to get the 4th term, 160 + 50 = 210.
And so on...
Notice that in the 2nd term, we added 1 copy of 50 to the 1st term.
In the 3rd, we ultimately added 2 copies of 50 to the 1st term.
In the 4th, we added 3 50s.
And so on... If the pattern continues, then the <em>n</em>-th term can be obtained by adding (<em>n</em> - 1) copies of 50 to the first term.
So, the 100th term is
60 + (100 - 1) * 50 = 5010
