156, 506,?, 1806

From the above given series , we have
First term + 350 = Second term
⇒ 156 + 350 = 506
Second term + 550 = third term
⇒ 506 + 550 = ? ⇒ ? = 1056
From the given figure , we get the value of third term ( ? ) = 1056
Third term + 550 = Fourth term
⇒ 1056 + 750 = 1806