$5^{th}$ degree polynomial expression $p(x)$ is a $5$ degree polynomial such that
$p(1)=1,p(2)=1,p(3)=2,p(4)=3,p(5)=5,p(6)=8,$ then $p(7)$

$\bf{My\; Try::}$ Here We can not write the given polynomial as $p(x)=x$
and $p(x)=ax^5+bx^4+cx^3+dx^2+ex+f$ for a very complex system of equation,
plz hel me how can i solve that question, Thanks
Like this problem, using difference of differences method,
Substitute $x$ for the appropriate values in your expression $$p(x)=ax^5+bx^4+cx^3+dx^2+ex+f$$and you will have a system of linear equations in $6$ variables ($a,b,c,d,e,f)$ that can be dealt with your favorite method, including linear algebra tech.

For instance, $p(2)=1$ yields $32a+16b+8c+4d+2e+f=1$.

After solving said system, you will have an explicit formula for $p(x)$, and then all you have to do is plug $x=7$ into it to obtain $p(7)$.