Dad and Xiao Ming run around the stadium. Dad takes 5 minutes to run a lap, and Xiao Ming takes 4 minutes to run a lap. The two started in the same direction from the starting point at the same time, and Xiao Ming was 45 meters away from his father when he finished a lap. How many meters is the circumference of the stadium?
爸爸和小明围着体育场跑步，爸爸跑一圈用5分钟，小明跑一圈用4分钟．二人从起点同时同向出发，小明跑完一圈时和爸爸相距45米．体育场一圈长多少米？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">45 / (1/5)</gadget>
<output>225</output>

<result>225</result>