Answer:
Step-by-step explanation:

Your answer would be 288. Also, did you mean 8/9? Hope I helped!
14 + 28 + 42 + 56 + … 280
= 14 (1 + 2 + 3 + 4 + … + 20)
= 14 × 20 × 21 / 2
= 2940
where we use the well-known identity,

Answer:
± 3
Step-by-step explanation:
let n be the number then the number squared is n² , so
6n² = 54 ( divide both sides by 6 )
n² = 9 ( take the square root of both sides )
n = ±
= ± 3
That is the number is 3 or - 3