3. A number consists of only two digits: 3 or 4, and both 3 and 4 must appear at least once. This number is a multiple of both 3 and 4. The smallest such number is $\qquad$ .
【Answer】 3444

【Solution】To make it a multiple of 4, the last two digits can only be 44. If there are only two digits 4, this number cannot be a multiple of 3, so it is easy to get its minimum value as 3444