Twice the difference between a number, x, and fifteen is three times the number.

Answer 1

"The difference between a number x and 15" -----> (x - 15)

"Twice that difference" ------> 2(x - 15)

"is three times the number -------> 2(x - 15) = 3x

2x - 30 = 3x

-2x -2x

-30 = x

Answer 2

2(x-15) = 3x

2x-30 =3x

3x-2x = -30

x = -30

or possibly

2(15-x) = 3x

30-2x = 3x

3x+2x = 30

5x =30

x =30/5 = 6

go with -30, but 6 is also a possible answer, depending on the what problem is asking