25X(59+59+59+59)=25x(4x59)=25x4x59=100x59=5900
25X（59+59+59+59)=25X59X4=100X59=5900
25x（60＋60＋60＋60）－25X4＝1500x4－25x4＝6000－100＝5900
=25×4×59
