Answer:
6
Step-by-step explanation:
we start with:
n(n + 1) + 3 = 45
n² + 1n = 42
n² + 1n - 42 = 0
n can be either 6 or -7
(n - 6)(n + 7)
since we cannot have negative numbers, the answer should be 6, but we can verify which number fits our equation:
n = 7 ⇒ n(n + 1) + 3 = 45
7(7 + 1) + 3 = 59 WRONG
n = 6 ⇒ n(n + 1) + 3 = 45
6(6 + 1) + 3 = 45 ✓ CORRECT
