Which expression represents the sum of 8 and twice a number
8+n
8+2n
8×2n
2×(8+n)

8 + 2 n (second expression listed)

Explanation:

Since we don't know the number, we represent it with a letter (n).

Twice a number (two times that number) will therefore be: 2 n.

and the addition (sum) of 8 to such will lead to 8 + 2 n

The sum of 8 and twice a number is : 8 + 2 n

at positions a, g kinetic energy is maximum.

at position d, potential energy is maximum.