4. In Beijing, there is a restaurant named “Tian Ran Ju”, which has a famous couplet inside: "Guests ascend to Tian Ran Ju, surprisingly they are guests from the sky." Coincidentally, this couplet can form a multiplication equation (see the figure below). The same Chinese characters represent the same digits, while different characters represent different digits. "Tian Ran Ju" expressed as a three-digit number is $\qquad$
Answer: 978