Answer:
7
Explanation:
let the number be n then twice the number is 2n and difference between it and 8 is 2n - 8. Tripling this and equating to 18 is then
3(2n - 8) = 18 ( divide both sides by 3 )
2n - 8 = 6 ( add 8 to both sides )
2n = 14 ( divide both sides by 2 )
n = 7
the unknown number is 7