Answer:
[tex]4^{th} +5^{th} = 58[/tex]
Step-by-step explanation:
What we have here is a Sequence, where there is no common difference. By making the 1 + 2 as the 1st term added to 2nd term, and the 3+4 as the 3rd +4th term and so on, etc.
[tex](21,36,43, 58,65,80...)\\a_{2}-a_{1}=15 \:\\a_{3}-a_{2}=7\: (21+15=36)\\a_{4}-a_{3}=15\:(36+15=43)\\a_{5}-a_{4}=7\:(43+15=58)\\[/tex]
So, as we can see the difference between the 4th and 5th term will be 15. Just add 15 to 43, we'll have 58
