a@b=(a, b)+(a, b), where (a, b) represents the least common multiple of a and b, (a, b) represents the greatest common divisor of a and b, known 12@x= 42. Find x.
a@b=(a，b)+(a，b)，其中(a，b)表示a与b的最小公倍数，(a，b)表示a与b的最大公约数，已知12@x=42，求x．
<result>18</result>