Each term adds 9 to the previous term.
The first term is 57, and to find the 250th term, we'd add 9 a total of 249 times.
That's the same as adding 9 times 249, which is 2241.
57 + 2241 = 2298.
(By the way, you can represent any term \(a_n\) of this equation with the expression \(48+9n\). What we do is count one step back to find our "zeroth" term, per se, and then each addition is represented as 9 times the n. This could also be \(57+a_{n-1}\).)
