[7/8+4/9] ÷ 1/72 = [7/8+4/9] * 72 = 7/8* 72 +4/9* 72 = 63+32 = 95
1/8÷1/5-5/8x10/11 = 1/8 * 5 - 5/8x10/11= 5/8 - 1/44 =（55-2)/88 = 53/88
7/15÷14÷2/3 = 7/15 * 1/14* 3/2 = 1/5 * 1/2 *1/2 = 1/20
3/4÷12 * 16/21+3/14 = 3/4 *1/12 * 16/21+3/14 = 1/1 *1/1 * 1/21+3/14 = （2+3*3)/42 = 11/42
7/8÷[2/5+1/20] * 4/21 = 7/8 ÷ 5/20 * 4/21 = 7/8 *4 * 4/21 = 1/1 *1 * 2/3 = 2/3