The general equation for an aritmetic sequence is $t\left(n\right) = mn + b$.

Use $t\left(8\right) = 1056$ to write an equation.
$t\left(8\right) = m\left(8\right) + b$ or $1056 = 8m + b$

Use $t\left(13\right) = 116$ to write another equation.

Solve the system of equations you wrote for $m$ and $b$.

$t\left(n\right) = −188n + 2560$

To find $t\left(5\right)$, substitute $5$ for $n$ in the equation that you wrote.