What is the question exactly?
Answer:
an = 4n +5
Step-by-step explanation:
First we need to find a common difference
d = a2-a1 = 13-9 = 4
The formula for an
an =a1+d(n-1)
an = 9 + 4(n-1)
Distributing
an = 9+4n-4
Combine like terms
an = 4n +5
Answer: 
Step-by-step explanation:
See attached image, it's direct formula substitution.
90 or 100 something like that.
<span> The triangle seems to be a scalene triangle because all three of its sides are different. </span>