Twice the quantity of seven plus x is the same as the difference of x and seven

seven plus x
7 + x

Twice the quantity of seven plus x
2(7 + x)

Difference of x and seven
x - 7

The phrase is the same as means equal to. This is our algebraic expression:
2(7 + x) = x - 7

If the problem asks you to solve for x, distribute 2 on the left side:
14 + 2x = x - 7

Subtract x from the right side
14 + x = -7

Subtract 14 from each side
x = -21