Straight-Line Depreciation. A company buys a copier for $\$ 5200$ on January 1 of a given year. The machine is expected to last for 8 years, at the end of which time its trade-in, or salvage, value will be
$\$ 1100 .$ If the company figures the decline in value to be the same each year, then the trade-in values, after $t$ years, $0 \leq t \leq 8,$ form an arithmetic sequence given by
$$
a_{t}=C-t\left(\frac{C-S}{N}\right)
$$
where $C$ is the original cost of the item, $N$ the years of expected life, and $S$ the salvage value.
a) Find the formula for $a_{r}$ for the straight-line depreciation of the copier.
b) Find the trade-in value after 0 year, 1 year,
2 years, 3 years, 4 years, 7 years, and 8 years.
c) Find a formula that expresses $a$, recursively.